tablefunc.c

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/*
 * contrib/tablefunc/tablefunc.c
 *
 *
 * tablefunc
 *
 * Sample to demonstrate C functions which return setof scalar
 * and setof composite.
 * Joe Conway <mail@joeconway.com>
 * And contributors:
 * Nabil Sayegh <postgresql@e-trolley.de>
 *
 * Copyright (c) 2002-2021, PostgreSQL Global Development Group
 *
 * Permission to use, copy, modify, and distribute this software and its
 * documentation for any purpose, without fee, and without a written agreement
 * is hereby granted, provided that the above copyright notice and this
 * paragraph and the following two paragraphs appear in all copies.
 *
 * IN NO EVENT SHALL THE AUTHORS OR DISTRIBUTORS BE LIABLE TO ANY PARTY FOR
 * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
 * LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
 * DOCUMENTATION, EVEN IF THE AUTHOR OR DISTRIBUTORS HAVE BEEN ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 * THE AUTHORS AND DISTRIBUTORS SPECIFICALLY DISCLAIM ANY WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
 * ON AN "AS IS" BASIS, AND THE AUTHOR AND DISTRIBUTORS HAS NO OBLIGATIONS TO
 * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
 *
 */
#include "postgres.h"

#include <math.h>

#include "access/htup_details.h"
#include "catalog/pg_type.h"
#include "executor/spi.h"
#include "funcapi.h"
#include "lib/stringinfo.h"
#include "miscadmin.h"
#include "tablefunc.h"
#include "utils/builtins.h"

PG_MODULE_MAGIC;

static HTAB *load_categories_hash(char *cats_sql, MemoryContext per_query_ctx);
static Tuplestorestate *get_crosstab_tuplestore(char *sql,
                                                HTAB *crosstab_hash,
                                                TupleDesc tupdesc,
                                                bool randomAccess);
static void validateConnectbyTupleDesc(TupleDesc tupdesc, bool show_branch, bool show_serial);
static bool compatCrosstabTupleDescs(TupleDesc tupdesc1, TupleDesc tupdesc2);
static void compatConnectbyTupleDescs(TupleDesc tupdesc1, TupleDesc tupdesc2);
static void get_normal_pair(float8 *x1, float8 *x2);
static Tuplestorestate *connectby(char *relname,
                                  char *key_fld,
                                  char *parent_key_fld,
                                  char *orderby_fld,
                                  char *branch_delim,
                                  char *start_with,
                                  int max_depth,
                                  bool show_branch,
                                  bool show_serial,
                                  MemoryContext per_query_ctx,
                                  bool randomAccess,
                                  AttInMetadata *attinmeta);
static void build_tuplestore_recursively(char *key_fld,
                                         char *parent_key_fld,
                                         char *relname,
                                         char *orderby_fld,
                                         char *branch_delim,
                                         char *start_with,
                                         char *branch,
                                         int level,
                                         int *serial,
                                         int max_depth,
                                         bool show_branch,
                                         bool show_serial,
                                         MemoryContext per_query_ctx,
                                         AttInMetadata *attinmeta,
                                         Tuplestorestate *tupstore);

typedef struct
{
    float8      mean;           /* mean of the distribution */
    float8      stddev;         /* stddev of the distribution */
    float8      carry_val;      /* hold second generated value */
    bool        use_carry;      /* use second generated value */
} normal_rand_fctx;

#define xpfree(var_) \
    do { \
        if (var_ != NULL) \
        { \
            pfree(var_); \
            var_ = NULL; \
        } \
    } while (0)

#define xpstrdup(tgtvar_, srcvar_) \
    do { \
        if (srcvar_) \
            tgtvar_ = pstrdup(srcvar_); \
        else \
            tgtvar_ = NULL; \
    } while (0)

#define xstreq(tgtvar_, srcvar_) \
    (((tgtvar_ == NULL) && (srcvar_ == NULL)) || \
     ((tgtvar_ != NULL) && (srcvar_ != NULL) && (strcmp(tgtvar_, srcvar_) == 0)))

/* sign, 10 digits, '\0' */
#define INT32_STRLEN    12

/* stored info for a crosstab category */
typedef struct crosstab_cat_desc
{
    char       *catname;        /* full category name */
    uint64      attidx;         /* zero based */
} crosstab_cat_desc;

#define MAX_CATNAME_LEN         NAMEDATALEN
#define INIT_CATS               64

#define crosstab_HashTableLookup(HASHTAB, CATNAME, CATDESC) \
do { \
    crosstab_HashEnt *hentry; char key[MAX_CATNAME_LEN]; \
    \
    MemSet(key, 0, MAX_CATNAME_LEN); \
    snprintf(key, MAX_CATNAME_LEN - 1, "%s", CATNAME); \
    hentry = (crosstab_HashEnt*) hash_search(HASHTAB, \
                                         key, HASH_FIND, NULL); \
    if (hentry) \
        CATDESC = hentry->catdesc; \
    else \
        CATDESC = NULL; \
} while(0)

#define crosstab_HashTableInsert(HASHTAB, CATDESC) \
do { \
    crosstab_HashEnt *hentry; bool found; char key[MAX_CATNAME_LEN]; \
    \
    MemSet(key, 0, MAX_CATNAME_LEN); \
    snprintf(key, MAX_CATNAME_LEN - 1, "%s", CATDESC->catname); \
    hentry = (crosstab_HashEnt*) hash_search(HASHTAB, \
                                         key, HASH_ENTER, &found); \
    if (found) \
        ereport(ERROR, \
                (errcode(ERRCODE_DUPLICATE_OBJECT), \
                 errmsg("duplicate category name"))); \
    hentry->catdesc = CATDESC; \
} while(0)

/* hash table */
typedef struct crosstab_hashent
{
    char        internal_catname[MAX_CATNAME_LEN];
    crosstab_cat_desc *catdesc;
} crosstab_HashEnt;

/*
 * normal_rand - return requested number of random values
 * with a Gaussian (Normal) distribution.
 *
 * inputs are int numvals, float8 mean, and float8 stddev
 * returns setof float8
 */
PG_FUNCTION_INFO_V1(normal_rand);
Datum
normal_rand(PG_FUNCTION_ARGS)
{
    FuncCallContext *funcctx;
    uint64      call_cntr;
    uint64      max_calls;
    normal_rand_fctx *fctx;
    float8      mean;
    float8      stddev;
    float8      carry_val;
    bool        use_carry;
    MemoryContext oldcontext;

    /* stuff done only on the first call of the function */
    if (SRF_IS_FIRSTCALL())
    {
        int32       num_tuples;

        /* create a function context for cross-call persistence */
        funcctx = SRF_FIRSTCALL_INIT();

        /*
         * switch to memory context appropriate for multiple function calls
         */
        oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);

        /* total number of tuples to be returned */
        num_tuples = PG_GETARG_INT32(0);
        if (num_tuples < 0)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("number of rows cannot be negative")));
        funcctx->max_calls = num_tuples;

        /* allocate memory for user context */
        fctx = (normal_rand_fctx *) palloc(sizeof(normal_rand_fctx));

        /*
         * Use fctx to keep track of upper and lower bounds from call to call.
         * It will also be used to carry over the spare value we get from the
         * Box-Muller algorithm so that we only actually calculate a new value
         * every other call.
         */
        fctx->mean = PG_GETARG_FLOAT8(1);
        fctx->stddev = PG_GETARG_FLOAT8(2);
        fctx->carry_val = 0;
        fctx->use_carry = false;

        funcctx->user_fctx = fctx;

        MemoryContextSwitchTo(oldcontext);
    }

    /* stuff done on every call of the function */
    funcctx = SRF_PERCALL_SETUP();

    call_cntr = funcctx->call_cntr;
    max_calls = funcctx->max_calls;
    fctx = funcctx->user_fctx;
    mean = fctx->mean;
    stddev = fctx->stddev;
    carry_val = fctx->carry_val;
    use_carry = fctx->use_carry;

    if (call_cntr < max_calls)  /* do when there is more left to send */
    {
        float8      result;

        if (use_carry)
        {
            /*
             * reset use_carry and use second value obtained on last pass
             */
            fctx->use_carry = false;
            result = carry_val;
        }
        else
        {
            float8      normval_1;
            float8      normval_2;

            /* Get the next two normal values */
            get_normal_pair(&normval_1, &normval_2);

            /* use the first */
            result = mean + (stddev * normval_1);

            /* and save the second */
            fctx->carry_val = mean + (stddev * normval_2);
            fctx->use_carry = true;
        }

        /* send the result */
        SRF_RETURN_NEXT(funcctx, Float8GetDatum(result));
    }
    else
        /* do when there is no more left */
        SRF_RETURN_DONE(funcctx);
}

/*
 * get_normal_pair()
 * Assigns normally distributed (Gaussian) values to a pair of provided
 * parameters, with mean 0, standard deviation 1.
 *
 * This routine implements Algorithm P (Polar method for normal deviates)
 * from Knuth's _The_Art_of_Computer_Programming_, Volume 2, 3rd ed., pages
 * 122-126. Knuth cites his source as "The polar method", G. E. P. Box, M. E.
 * Muller, and G. Marsaglia, _Annals_Math,_Stat._ 29 (1958), 610-611.
 *
 */
static void
get_normal_pair(float8 *x1, float8 *x2)
{
    float8      u1,
                u2,
                v1,
                v2,
                s;

    do
    {
        u1 = (float8) random() / (float8) MAX_RANDOM_VALUE;
        u2 = (float8) random() / (float8) MAX_RANDOM_VALUE;

        v1 = (2.0 * u1) - 1.0;
        v2 = (2.0 * u2) - 1.0;

        s = v1 * v1 + v2 * v2;
    } while (s >= 1.0);

    if (s == 0)
    {
        *x1 = 0;
        *x2 = 0;
    }
    else
    {
        s = sqrt((-2.0 * log(s)) / s);
        *x1 = v1 * s;
        *x2 = v2 * s;
    }
}

/*
 * crosstab - create a crosstab of rowids and values columns from a
 * SQL statement returning one rowid column, one category column,
 * and one value column.
 *
 * e.g. given sql which produces:
 *
 *          rowid   cat     value
 *          ------+-------+-------
 *          row1    cat1    val1
 *          row1    cat2    val2
 *          row1    cat3    val3
 *          row1    cat4    val4
 *          row2    cat1    val5
 *          row2    cat2    val6
 *          row2    cat3    val7
 *          row2    cat4    val8
 *
 * crosstab returns:
 *                  <===== values columns =====>
 *          rowid   cat1    cat2    cat3    cat4
 *          ------+-------+-------+-------+-------
 *          row1    val1    val2    val3    val4
 *          row2    val5    val6    val7    val8
 *
 * NOTES:
 * 1. SQL result must be ordered by 1,2.
 * 2. The number of values columns depends on the tuple description
 *    of the function's declared return type.  The return type's columns
 *    must match the datatypes of the SQL query's result.  The datatype
 *    of the category column can be anything, however.
 * 3. Missing values (i.e. not enough adjacent rows of same rowid to
 *    fill the number of result values columns) are filled in with nulls.
 * 4. Extra values (i.e. too many adjacent rows of same rowid to fill
 *    the number of result values columns) are skipped.
 * 5. Rows with all nulls in the values columns are skipped.
 */
PG_FUNCTION_INFO_V1(crosstab);
Datum
crosstab(PG_FUNCTION_ARGS)
{
    char       *sql = text_to_cstring(PG_GETARG_TEXT_PP(0));
    ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
    Tuplestorestate *tupstore;
    TupleDesc   tupdesc;
    uint64      call_cntr;
    uint64      max_calls;
    AttInMetadata *attinmeta;
    SPITupleTable *spi_tuptable;
    TupleDesc   spi_tupdesc;
    bool        firstpass;
    char       *lastrowid;
    int         i;
    int         num_categories;
    MemoryContext per_query_ctx;
    MemoryContext oldcontext;
    int         ret;
    uint64      proc;

    /* check to see if caller supports us returning a tuplestore */
    if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("set-valued function called in context that cannot accept a set")));
    if (!(rsinfo->allowedModes & SFRM_Materialize))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("materialize mode required, but it is not allowed in this context")));

    per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;

    /* Connect to SPI manager */
    if ((ret = SPI_connect()) < 0)
        /* internal error */
        elog(ERROR, "crosstab: SPI_connect returned %d", ret);

    /* Retrieve the desired rows */
    ret = SPI_execute(sql, true, 0);
    proc = SPI_processed;

    /* If no qualifying tuples, fall out early */
    if (ret != SPI_OK_SELECT || proc == 0)
    {
        SPI_finish();
        rsinfo->isDone = ExprEndResult;
        PG_RETURN_NULL();
    }

    spi_tuptable = SPI_tuptable;
    spi_tupdesc = spi_tuptable->tupdesc;

    /*----------
     * The provided SQL query must always return three columns.
     *
     * 1. rowname
     *  the label or identifier for each row in the final result
     * 2. category
     *  the label or identifier for each column in the final result
     * 3. values
     *  the value for each column in the final result
     *----------
     */
    if (spi_tupdesc->natts != 3)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid source data SQL statement"),
                 errdetail("The provided SQL must return 3 "
                           "columns: rowid, category, and values.")));

    /* get a tuple descriptor for our result type */
    switch (get_call_result_type(fcinfo, NULL, &tupdesc))
    {
        case TYPEFUNC_COMPOSITE:
            /* success */
            break;
        case TYPEFUNC_RECORD:
            /* failed to determine actual type of RECORD */
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("function returning record called in context "
                            "that cannot accept type record")));
            break;
        default:
            /* result type isn't composite */
            ereport(ERROR,
                    (errcode(ERRCODE_DATATYPE_MISMATCH),
                     errmsg("return type must be a row type")));
            break;
    }

    /*
     * Check that return tupdesc is compatible with the data we got from SPI,
     * at least based on number and type of attributes
     */
    if (!compatCrosstabTupleDescs(tupdesc, spi_tupdesc))
        ereport(ERROR,
                (errcode(ERRCODE_SYNTAX_ERROR),
                 errmsg("return and sql tuple descriptions are " \
                        "incompatible")));

    /*
     * switch to long-lived memory context
     */
    oldcontext = MemoryContextSwitchTo(per_query_ctx);

    /* make sure we have a persistent copy of the result tupdesc */
    tupdesc = CreateTupleDescCopy(tupdesc);

    /* initialize our tuplestore in long-lived context */
    tupstore =
        tuplestore_begin_heap(rsinfo->allowedModes & SFRM_Materialize_Random,
                              false, work_mem);

    MemoryContextSwitchTo(oldcontext);

    /*
     * Generate attribute metadata needed later to produce tuples from raw C
     * strings
     */
    attinmeta = TupleDescGetAttInMetadata(tupdesc);

    /* total number of tuples to be examined */
    max_calls = proc;

    /* the return tuple always must have 1 rowid + num_categories columns */
    num_categories = tupdesc->natts - 1;

    firstpass = true;
    lastrowid = NULL;

    for (call_cntr = 0; call_cntr < max_calls; call_cntr++)
    {
        bool        skip_tuple = false;
        char      **values;

        /* allocate and zero space */
        values = (char **) palloc0((1 + num_categories) * sizeof(char *));

        /*
         * now loop through the sql results and assign each value in sequence
         * to the next category
         */
        for (i = 0; i < num_categories; i++)
        {
            HeapTuple   spi_tuple;
            char       *rowid;

            /* see if we've gone too far already */
            if (call_cntr >= max_calls)
                break;

            /* get the next sql result tuple */
            spi_tuple = spi_tuptable->vals[call_cntr];

            /* get the rowid from the current sql result tuple */
            rowid = SPI_getvalue(spi_tuple, spi_tupdesc, 1);

            /*
             * If this is the first pass through the values for this rowid,
             * set the first column to rowid
             */
            if (i == 0)
            {
                xpstrdup(values[0], rowid);

                /*
                 * Check to see if the rowid is the same as that of the last
                 * tuple sent -- if so, skip this tuple entirely
                 */
                if (!firstpass && xstreq(lastrowid, rowid))
                {
                    xpfree(rowid);
                    skip_tuple = true;
                    break;
                }
            }

            /*
             * If rowid hasn't changed on us, continue building the output
             * tuple.
             */
            if (xstreq(rowid, values[0]))
            {
                /*
                 * Get the next category item value, which is always attribute
                 * number three.
                 *
                 * Be careful to assign the value to the array index based on
                 * which category we are presently processing.
                 */
                values[1 + i] = SPI_getvalue(spi_tuple, spi_tupdesc, 3);

                /*
                 * increment the counter since we consume a row for each
                 * category, but not for last pass because the outer loop will
                 * do that for us
                 */
                if (i < (num_categories - 1))
                    call_cntr++;
                xpfree(rowid);
            }
            else
            {
                /*
                 * We'll fill in NULLs for the missing values, but we need to
                 * decrement the counter since this sql result row doesn't
                 * belong to the current output tuple.
                 */
                call_cntr--;
                xpfree(rowid);
                break;
            }
        }

        if (!skip_tuple)
        {
            HeapTuple   tuple;

            /* build the tuple and store it */
            tuple = BuildTupleFromCStrings(attinmeta, values);
            tuplestore_puttuple(tupstore, tuple);
            heap_freetuple(tuple);
        }

        /* Remember current rowid */
        xpfree(lastrowid);
        xpstrdup(lastrowid, values[0]);
        firstpass = false;

        /* Clean up */
        for (i = 0; i < num_categories + 1; i++)
            if (values[i] != NULL)
                pfree(values[i]);
        pfree(values);
    }

    /* let the caller know we're sending back a tuplestore */
    rsinfo->returnMode = SFRM_Materialize;
    rsinfo->setResult = tupstore;
    rsinfo->setDesc = tupdesc;

    /* release SPI related resources (and return to caller's context) */
    SPI_finish();

    return (Datum) 0;
}

/*
 * crosstab_hash - reimplement crosstab as materialized function and
 * properly deal with missing values (i.e. don't pack remaining
 * values to the left)
 *
 * crosstab - create a crosstab of rowids and values columns from a
 * SQL statement returning one rowid column, one category column,
 * and one value column.
 *
 * e.g. given sql which produces:
 *
 *          rowid   cat     value
 *          ------+-------+-------
 *          row1    cat1    val1
 *          row1    cat2    val2
 *          row1    cat4    val4
 *          row2    cat1    val5
 *          row2    cat2    val6
 *          row2    cat3    val7
 *          row2    cat4    val8
 *
 * crosstab returns:
 *                  <===== values columns =====>
 *          rowid   cat1    cat2    cat3    cat4
 *          ------+-------+-------+-------+-------
 *          row1    val1    val2    null    val4
 *          row2    val5    val6    val7    val8
 *
 * NOTES:
 * 1. SQL result must be ordered by 1.
 * 2. The number of values columns depends on the tuple description
 *    of the function's declared return type.
 * 3. Missing values (i.e. missing category) are filled in with nulls.
 * 4. Extra values (i.e. not in category results) are skipped.
 */
PG_FUNCTION_INFO_V1(crosstab_hash);
Datum
crosstab_hash(PG_FUNCTION_ARGS)
{
    char       *sql = text_to_cstring(PG_GETARG_TEXT_PP(0));
    char       *cats_sql = text_to_cstring(PG_GETARG_TEXT_PP(1));
    ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
    TupleDesc   tupdesc;
    MemoryContext per_query_ctx;
    MemoryContext oldcontext;
    HTAB       *crosstab_hash;

    /* check to see if caller supports us returning a tuplestore */
    if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("set-valued function called in context that cannot accept a set")));
    if (!(rsinfo->allowedModes & SFRM_Materialize) ||
        rsinfo->expectedDesc == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("materialize mode required, but it is not allowed in this context")));

    per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
    oldcontext = MemoryContextSwitchTo(per_query_ctx);

    /* get the requested return tuple description */
    tupdesc = CreateTupleDescCopy(rsinfo->expectedDesc);

    /*
     * Check to make sure we have a reasonable tuple descriptor
     *
     * Note we will attempt to coerce the values into whatever the return
     * attribute type is and depend on the "in" function to complain if
     * needed.
     */
    if (tupdesc->natts < 2)
        ereport(ERROR,
                (errcode(ERRCODE_SYNTAX_ERROR),
                 errmsg("query-specified return tuple and " \
                        "crosstab function are not compatible")));

    /* load up the categories hash table */
    crosstab_hash = load_categories_hash(cats_sql, per_query_ctx);

    /* let the caller know we're sending back a tuplestore */
    rsinfo->returnMode = SFRM_Materialize;

    /* now go build it */
    rsinfo->setResult = get_crosstab_tuplestore(sql,
                                                crosstab_hash,
                                                tupdesc,
                                                rsinfo->allowedModes & SFRM_Materialize_Random);

    /*
     * SFRM_Materialize mode expects us to return a NULL Datum. The actual
     * tuples are in our tuplestore and passed back through rsinfo->setResult.
     * rsinfo->setDesc is set to the tuple description that we actually used
     * to build our tuples with, so the caller can verify we did what it was
     * expecting.
     */
    rsinfo->setDesc = tupdesc;
    MemoryContextSwitchTo(oldcontext);

    return (Datum) 0;
}

/*
 * load up the categories hash table
 */
static HTAB *
load_categories_hash(char *cats_sql, MemoryContext per_query_ctx)
{
    HTAB       *crosstab_hash;
    HASHCTL     ctl;
    int         ret;
    uint64      proc;
    MemoryContext SPIcontext;

    /* initialize the category hash table */
    ctl.keysize = MAX_CATNAME_LEN;
    ctl.entrysize = sizeof(crosstab_HashEnt);
    ctl.hcxt = per_query_ctx;

    /*
     * use INIT_CATS, defined above as a guess of how many hash table entries
     * to create, initially
     */
    crosstab_hash = hash_create("crosstab hash",
                                INIT_CATS,
                                &ctl,
                                HASH_ELEM | HASH_STRINGS | HASH_CONTEXT);

    /* Connect to SPI manager */
    if ((ret = SPI_connect()) < 0)
        /* internal error */
        elog(ERROR, "load_categories_hash: SPI_connect returned %d", ret);

    /* Retrieve the category name rows */
    ret = SPI_execute(cats_sql, true, 0);
    proc = SPI_processed;

    /* Check for qualifying tuples */
    if ((ret == SPI_OK_SELECT) && (proc > 0))
    {
        SPITupleTable *spi_tuptable = SPI_tuptable;
        TupleDesc   spi_tupdesc = spi_tuptable->tupdesc;
        uint64      i;

        /*
         * The provided categories SQL query must always return one column:
         * category - the label or identifier for each column
         */
        if (spi_tupdesc->natts != 1)
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                     errmsg("provided \"categories\" SQL must " \
                            "return 1 column of at least one row")));

        for (i = 0; i < proc; i++)
        {
            crosstab_cat_desc *catdesc;
            char       *catname;
            HeapTuple   spi_tuple;

            /* get the next sql result tuple */
            spi_tuple = spi_tuptable->vals[i];

            /* get the category from the current sql result tuple */
            catname = SPI_getvalue(spi_tuple, spi_tupdesc, 1);
            if (catname == NULL)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("provided \"categories\" SQL must " \
                                "not return NULL values")));

            SPIcontext = MemoryContextSwitchTo(per_query_ctx);

            catdesc = (crosstab_cat_desc *) palloc(sizeof(crosstab_cat_desc));
            catdesc->catname = catname;
            catdesc->attidx = i;

            /* Add the proc description block to the hashtable */
            crosstab_HashTableInsert(crosstab_hash, catdesc);

            MemoryContextSwitchTo(SPIcontext);
        }
    }

    if (SPI_finish() != SPI_OK_FINISH)
        /* internal error */
        elog(ERROR, "load_categories_hash: SPI_finish() failed");

    return crosstab_hash;
}

/*
 * create and populate the crosstab tuplestore using the provided source query
 */
static Tuplestorestate *
get_crosstab_tuplestore(char *sql,
                        HTAB *crosstab_hash,
                        TupleDesc tupdesc,
                        bool randomAccess)
{
    Tuplestorestate *tupstore;
    int         num_categories = hash_get_num_entries(crosstab_hash);
    AttInMetadata *attinmeta = TupleDescGetAttInMetadata(tupdesc);
    char      **values;
    HeapTuple   tuple;
    int         ret;
    uint64      proc;

    /* initialize our tuplestore (while still in query context!) */
    tupstore = tuplestore_begin_heap(randomAccess, false, work_mem);

    /* Connect to SPI manager */
    if ((ret = SPI_connect()) < 0)
        /* internal error */
        elog(ERROR, "get_crosstab_tuplestore: SPI_connect returned %d", ret);

    /* Now retrieve the crosstab source rows */
    ret = SPI_execute(sql, true, 0);
    proc = SPI_processed;

    /* Check for qualifying tuples */
    if ((ret == SPI_OK_SELECT) && (proc > 0))
    {
        SPITupleTable *spi_tuptable = SPI_tuptable;
        TupleDesc   spi_tupdesc = spi_tuptable->tupdesc;
        int         ncols = spi_tupdesc->natts;
        char       *rowid;
        char       *lastrowid = NULL;
        bool        firstpass = true;
        uint64      i;
        int         j;
        int         result_ncols;

        if (num_categories == 0)
        {
            /* no qualifying category tuples */
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                     errmsg("provided \"categories\" SQL must " \
                            "return 1 column of at least one row")));
        }

        /*
         * The provided SQL query must always return at least three columns:
         *
         * 1. rowname   the label for each row - column 1 in the final result
         * 2. category  the label for each value-column in the final result 3.
         * value     the values used to populate the value-columns
         *
         * If there are more than three columns, the last two are taken as
         * "category" and "values". The first column is taken as "rowname".
         * Additional columns (2 thru N-2) are assumed the same for the same
         * "rowname", and are copied into the result tuple from the first time
         * we encounter a particular rowname.
         */
        if (ncols < 3)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("invalid source data SQL statement"),
                     errdetail("The provided SQL must return 3 " \
                               " columns; rowid, category, and values.")));

        result_ncols = (ncols - 2) + num_categories;

        /* Recheck to make sure we tuple descriptor still looks reasonable */
        if (tupdesc->natts != result_ncols)
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                     errmsg("invalid return type"),
                     errdetail("Query-specified return " \
                               "tuple has %d columns but crosstab " \
                               "returns %d.", tupdesc->natts, result_ncols)));

        /* allocate space and make sure it's clear */
        values = (char **) palloc0(result_ncols * sizeof(char *));

        for (i = 0; i < proc; i++)
        {
            HeapTuple   spi_tuple;
            crosstab_cat_desc *catdesc;
            char       *catname;

            /* get the next sql result tuple */
            spi_tuple = spi_tuptable->vals[i];

            /* get the rowid from the current sql result tuple */
            rowid = SPI_getvalue(spi_tuple, spi_tupdesc, 1);

            /*
             * if we're on a new output row, grab the column values up to
             * column N-2 now
             */
            if (firstpass || !xstreq(lastrowid, rowid))
            {
                /*
                 * a new row means we need to flush the old one first, unless
                 * we're on the very first row
                 */
                if (!firstpass)
                {
                    /* rowid changed, flush the previous output row */
                    tuple = BuildTupleFromCStrings(attinmeta, values);

                    tuplestore_puttuple(tupstore, tuple);

                    for (j = 0; j < result_ncols; j++)
                        xpfree(values[j]);
                }

                values[0] = rowid;
                for (j = 1; j < ncols - 2; j++)
                    values[j] = SPI_getvalue(spi_tuple, spi_tupdesc, j + 1);

                /* we're no longer on the first pass */
                firstpass = false;
            }

            /* look up the category and fill in the appropriate column */
            catname = SPI_getvalue(spi_tuple, spi_tupdesc, ncols - 1);

            if (catname != NULL)
            {
                crosstab_HashTableLookup(crosstab_hash, catname, catdesc);

                if (catdesc)
                    values[catdesc->attidx + ncols - 2] =
                        SPI_getvalue(spi_tuple, spi_tupdesc, ncols);
            }

            xpfree(lastrowid);
            xpstrdup(lastrowid, rowid);
        }

        /* flush the last output row */
        tuple = BuildTupleFromCStrings(attinmeta, values);

        tuplestore_puttuple(tupstore, tuple);
    }

    if (SPI_finish() != SPI_OK_FINISH)
        /* internal error */
        elog(ERROR, "get_crosstab_tuplestore: SPI_finish() failed");

    tuplestore_donestoring(tupstore);

    return tupstore;
}

/*
 * connectby_text - produce a result set from a hierarchical (parent/child)
 * table.
 *
 * e.g. given table foo:
 *
 *          keyid   parent_keyid pos
 *          ------+------------+--
 *          row1    NULL         0
 *          row2    row1         0
 *          row3    row1         0
 *          row4    row2         1
 *          row5    row2         0
 *          row6    row4         0
 *          row7    row3         0
 *          row8    row6         0
 *          row9    row5         0
 *
 *
 * connectby(text relname, text keyid_fld, text parent_keyid_fld
 *            [, text orderby_fld], text start_with, int max_depth
 *            [, text branch_delim])
 * connectby('foo', 'keyid', 'parent_keyid', 'pos', 'row2', 0, '~') returns:
 *
 *      keyid   parent_id   level    branch             serial
 *      ------+-----------+--------+-----------------------
 *      row2    NULL          0       row2                1
 *      row5    row2          1       row2~row5           2
 *      row9    row5          2       row2~row5~row9      3
 *      row4    row2          1       row2~row4           4
 *      row6    row4          2       row2~row4~row6      5
 *      row8    row6          3       row2~row4~row6~row8 6
 *
 */
PG_FUNCTION_INFO_V1(connectby_text);

#define CONNECTBY_NCOLS                 4
#define CONNECTBY_NCOLS_NOBRANCH        3

Datum
connectby_text(PG_FUNCTION_ARGS)
{
    char       *relname = text_to_cstring(PG_GETARG_TEXT_PP(0));
    char       *key_fld = text_to_cstring(PG_GETARG_TEXT_PP(1));
    char       *parent_key_fld = text_to_cstring(PG_GETARG_TEXT_PP(2));
    char       *start_with = text_to_cstring(PG_GETARG_TEXT_PP(3));
    int         max_depth = PG_GETARG_INT32(4);
    char       *branch_delim = NULL;
    bool        show_branch = false;
    bool        show_serial = false;
    ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
    TupleDesc   tupdesc;
    AttInMetadata *attinmeta;
    MemoryContext per_query_ctx;
    MemoryContext oldcontext;

    /* check to see if caller supports us returning a tuplestore */
    if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("set-valued function called in context that cannot accept a set")));
    if (!(rsinfo->allowedModes & SFRM_Materialize) ||
        rsinfo->expectedDesc == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("materialize mode required, but it is not allowed in this context")));

    if (fcinfo->nargs == 6)
    {
        branch_delim = text_to_cstring(PG_GETARG_TEXT_PP(5));
        show_branch = true;
    }
    else
        /* default is no show, tilde for the delimiter */
        branch_delim = pstrdup("~");

    per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
    oldcontext = MemoryContextSwitchTo(per_query_ctx);

    /* get the requested return tuple description */
    tupdesc = CreateTupleDescCopy(rsinfo->expectedDesc);

    /* does it meet our needs */
    validateConnectbyTupleDesc(tupdesc, show_branch, show_serial);

    /* OK, use it then */
    attinmeta = TupleDescGetAttInMetadata(tupdesc);

    /* OK, go to work */
    rsinfo->returnMode = SFRM_Materialize;
    rsinfo->setResult = connectby(relname,
                                  key_fld,
                                  parent_key_fld,
                                  NULL,
                                  branch_delim,
                                  start_with,
                                  max_depth,
                                  show_branch,
                                  show_serial,
                                  per_query_ctx,
                                  rsinfo->allowedModes & SFRM_Materialize_Random,
                                  attinmeta);
    rsinfo->setDesc = tupdesc;

    MemoryContextSwitchTo(oldcontext);

    /*
     * SFRM_Materialize mode expects us to return a NULL Datum. The actual
     * tuples are in our tuplestore and passed back through rsinfo->setResult.
     * rsinfo->setDesc is set to the tuple description that we actually used
     * to build our tuples with, so the caller can verify we did what it was
     * expecting.
     */
    return (Datum) 0;
}

PG_FUNCTION_INFO_V1(connectby_text_serial);
Datum
connectby_text_serial(PG_FUNCTION_ARGS)
{
    char       *relname = text_to_cstring(PG_GETARG_TEXT_PP(0));
    char       *key_fld = text_to_cstring(PG_GETARG_TEXT_PP(1));
    char       *parent_key_fld = text_to_cstring(PG_GETARG_TEXT_PP(2));
    char       *orderby_fld = text_to_cstring(PG_GETARG_TEXT_PP(3));
    char       *start_with = text_to_cstring(PG_GETARG_TEXT_PP(4));
    int         max_depth = PG_GETARG_INT32(5);
    char       *branch_delim = NULL;
    bool        show_branch = false;
    bool        show_serial = true;
    ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
    TupleDesc   tupdesc;
    AttInMetadata *attinmeta;
    MemoryContext per_query_ctx;
    MemoryContext oldcontext;

    /* check to see if caller supports us returning a tuplestore */
    if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("set-valued function called in context that cannot accept a set")));
    if (!(rsinfo->allowedModes & SFRM_Materialize) ||
        rsinfo->expectedDesc == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("materialize mode required, but it is not allowed in this context")));

    if (fcinfo->nargs == 7)
    {
        branch_delim = text_to_cstring(PG_GETARG_TEXT_PP(6));
        show_branch = true;
    }
    else
        /* default is no show, tilde for the delimiter */
        branch_delim = pstrdup("~");

    per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
    oldcontext = MemoryContextSwitchTo(per_query_ctx);

    /* get the requested return tuple description */
    tupdesc = CreateTupleDescCopy(rsinfo->expectedDesc);

    /* does it meet our needs */
    validateConnectbyTupleDesc(tupdesc, show_branch, show_serial);

    /* OK, use it then */
    attinmeta = TupleDescGetAttInMetadata(tupdesc);

    /* OK, go to work */
    rsinfo->returnMode = SFRM_Materialize;
    rsinfo->setResult = connectby(relname,
                                  key_fld,
                                  parent_key_fld,
                                  orderby_fld,
                                  branch_delim,
                                  start_with,
                                  max_depth,
                                  show_branch,
                                  show_serial,
                                  per_query_ctx,
                                  rsinfo->allowedModes & SFRM_Materialize_Random,
                                  attinmeta);
    rsinfo->setDesc = tupdesc;

    MemoryContextSwitchTo(oldcontext);

    /*
     * SFRM_Materialize mode expects us to return a NULL Datum. The actual
     * tuples are in our tuplestore and passed back through rsinfo->setResult.
     * rsinfo->setDesc is set to the tuple description that we actually used
     * to build our tuples with, so the caller can verify we did what it was
     * expecting.
     */
    return (Datum) 0;
}


/*
 * connectby - does the real work for connectby_text()
 */
static Tuplestorestate *
connectby(char *relname,
          char *key_fld,
          char *parent_key_fld,
          char *orderby_fld,
          char *branch_delim,
          char *start_with,
          int max_depth,
          bool show_branch,
          bool show_serial,
          MemoryContext per_query_ctx,
          bool randomAccess,
          AttInMetadata *attinmeta)
{
    Tuplestorestate *tupstore = NULL;
    int         ret;
    MemoryContext oldcontext;

    int         serial = 1;

    /* Connect to SPI manager */
    if ((ret = SPI_connect()) < 0)
        /* internal error */
        elog(ERROR, "connectby: SPI_connect returned %d", ret);

    /* switch to longer term context to create the tuple store */
    oldcontext = MemoryContextSwitchTo(per_query_ctx);

    /* initialize our tuplestore */
    tupstore = tuplestore_begin_heap(randomAccess, false, work_mem);

    MemoryContextSwitchTo(oldcontext);

    /* now go get the whole tree */
    build_tuplestore_recursively(key_fld,
                                 parent_key_fld,
                                 relname,
                                 orderby_fld,
                                 branch_delim,
                                 start_with,
                                 start_with,    /* current_branch */
                                 0, /* initial level is 0 */
                                 &serial,   /* initial serial is 1 */
                                 max_depth,
                                 show_branch,
                                 show_serial,
                                 per_query_ctx,
                                 attinmeta,
                                 tupstore);

    SPI_finish();

    return tupstore;
}

static void
build_tuplestore_recursively(char *key_fld,
                             char *parent_key_fld,
                             char *relname,
                             char *orderby_fld,
                             char *branch_delim,
                             char *start_with,
                             char *branch,
                             int level,
                             int *serial,
                             int max_depth,
                             bool show_branch,
                             bool show_serial,
                             MemoryContext per_query_ctx,
                             AttInMetadata *attinmeta,
                             Tuplestorestate *tupstore)
{
    TupleDesc   tupdesc = attinmeta->tupdesc;
    int         ret;
    uint64      proc;
    int         serial_column;
    StringInfoData sql;
    char      **values;
    char       *current_key;
    char       *current_key_parent;
    char        current_level[INT32_STRLEN];
    char        serial_str[INT32_STRLEN];
    char       *current_branch;
    HeapTuple   tuple;

    if (max_depth > 0 && level > max_depth)
        return;

    initStringInfo(&sql);

    /* Build initial sql statement */
    if (!show_serial)
    {
        appendStringInfo(&sql, "SELECT %s, %s FROM %s WHERE %s = %s AND %s IS NOT NULL AND %s <> %s",
                         key_fld,
                         parent_key_fld,
                         relname,
                         parent_key_fld,
                         quote_literal_cstr(start_with),
                         key_fld, key_fld, parent_key_fld);
        serial_column = 0;
    }
    else
    {
        appendStringInfo(&sql, "SELECT %s, %s FROM %s WHERE %s = %s AND %s IS NOT NULL AND %s <> %s ORDER BY %s",
                         key_fld,
                         parent_key_fld,
                         relname,
                         parent_key_fld,
                         quote_literal_cstr(start_with),
                         key_fld, key_fld, parent_key_fld,
                         orderby_fld);
        serial_column = 1;
    }

    if (show_branch)
        values = (char **) palloc((CONNECTBY_NCOLS + serial_column) * sizeof(char *));
    else
        values = (char **) palloc((CONNECTBY_NCOLS_NOBRANCH + serial_column) * sizeof(char *));

    /* First time through, do a little setup */
    if (level == 0)
    {
        /* root value is the one we initially start with */
        values[0] = start_with;

        /* root value has no parent */
        values[1] = NULL;

        /* root level is 0 */
        sprintf(current_level, "%d", level);
        values[2] = current_level;

        /* root branch is just starting root value */
        if (show_branch)
            values[3] = start_with;

        /* root starts the serial with 1 */
        if (show_serial)
        {
            sprintf(serial_str, "%d", (*serial)++);
            if (show_branch)
                values[4] = serial_str;
            else
                values[3] = serial_str;
        }

        /* construct the tuple */
        tuple = BuildTupleFromCStrings(attinmeta, values);

        /* now store it */
        tuplestore_puttuple(tupstore, tuple);

        /* increment level */
        level++;
    }

    /* Retrieve the desired rows */
    ret = SPI_execute(sql.data, true, 0);
    proc = SPI_processed;

    /* Check for qualifying tuples */
    if ((ret == SPI_OK_SELECT) && (proc > 0))
    {
        HeapTuple   spi_tuple;
        SPITupleTable *tuptable = SPI_tuptable;
        TupleDesc   spi_tupdesc = tuptable->tupdesc;
        uint64      i;
        StringInfoData branchstr;
        StringInfoData chk_branchstr;
        StringInfoData chk_current_key;

        /*
         * Check that return tupdesc is compatible with the one we got from
         * the query.
         */
        compatConnectbyTupleDescs(tupdesc, spi_tupdesc);

        initStringInfo(&branchstr);
        initStringInfo(&chk_branchstr);
        initStringInfo(&chk_current_key);

        for (i = 0; i < proc; i++)
        {
            /* initialize branch for this pass */
            appendStringInfoString(&branchstr, branch);
            appendStringInfo(&chk_branchstr, "%s%s%s", branch_delim, branch, branch_delim);

            /* get the next sql result tuple */
            spi_tuple = tuptable->vals[i];

            /* get the current key (might be NULL) */
            current_key = SPI_getvalue(spi_tuple, spi_tupdesc, 1);

            /* get the parent key (might be NULL) */
            current_key_parent = SPI_getvalue(spi_tuple, spi_tupdesc, 2);

            /* get the current level */
            sprintf(current_level, "%d", level);

            /* check to see if this key is also an ancestor */
            if (current_key)
            {
                appendStringInfo(&chk_current_key, "%s%s%s",
                                 branch_delim, current_key, branch_delim);
                if (strstr(chk_branchstr.data, chk_current_key.data))
                    ereport(ERROR,
                            (errcode(ERRCODE_INVALID_RECURSION),
                             errmsg("infinite recursion detected")));
            }

            /* OK, extend the branch */
            if (current_key)
                appendStringInfo(&branchstr, "%s%s", branch_delim, current_key);
            current_branch = branchstr.data;

            /* build a tuple */
            values[0] = current_key;
            values[1] = current_key_parent;
            values[2] = current_level;
            if (show_branch)
                values[3] = current_branch;
            if (show_serial)
            {
                sprintf(serial_str, "%d", (*serial)++);
                if (show_branch)
                    values[4] = serial_str;
                else
                    values[3] = serial_str;
            }

            tuple = BuildTupleFromCStrings(attinmeta, values);

            /* store the tuple for later use */
            tuplestore_puttuple(tupstore, tuple);

            heap_freetuple(tuple);

            /* recurse using current_key as the new start_with */
            if (current_key)
                build_tuplestore_recursively(key_fld,
                                             parent_key_fld,
                                             relname,
                                             orderby_fld,
                                             branch_delim,
                                             current_key,
                                             current_branch,
                                             level + 1,
                                             serial,
                                             max_depth,
                                             show_branch,
                                             show_serial,
                                             per_query_ctx,
                                             attinmeta,
                                             tupstore);

            xpfree(current_key);
            xpfree(current_key_parent);

            /* reset branch for next pass */
            resetStringInfo(&branchstr);
            resetStringInfo(&chk_branchstr);
            resetStringInfo(&chk_current_key);
        }

        xpfree(branchstr.data);
        xpfree(chk_branchstr.data);
        xpfree(chk_current_key.data);
    }
}

/*
 * Check expected (query runtime) tupdesc suitable for Connectby
 */
static void
validateConnectbyTupleDesc(TupleDesc td, bool show_branch, bool show_serial)
{
    int         serial_column = 0;

    if (show_serial)
        serial_column = 1;

    /* are there the correct number of columns */
    if (show_branch)
    {
        if (td->natts != (CONNECTBY_NCOLS + serial_column))
            ereport(ERROR,
                    (errcode(ERRCODE_DATATYPE_MISMATCH),
                     errmsg("invalid return type"),
                     errdetail("Query-specified return tuple has " \
                               "wrong number of columns.")));
    }
    else
    {
        if (td->natts != CONNECTBY_NCOLS_NOBRANCH + serial_column)
            ereport(ERROR,
                    (errcode(ERRCODE_DATATYPE_MISMATCH),
                     errmsg("invalid return type"),
                     errdetail("Query-specified return tuple has " \
                               "wrong number of columns.")));
    }

    /* check that the types of the first two columns match */
    if (TupleDescAttr(td, 0)->atttypid != TupleDescAttr(td, 1)->atttypid)
        ereport(ERROR,
                (errcode(ERRCODE_DATATYPE_MISMATCH),
                 errmsg("invalid return type"),
                 errdetail("First two columns must be the same type.")));

    /* check that the type of the third column is INT4 */
    if (TupleDescAttr(td, 2)->atttypid != INT4OID)
        ereport(ERROR,
                (errcode(ERRCODE_DATATYPE_MISMATCH),
                 errmsg("invalid return type"),
                 errdetail("Third column must be type %s.",
                           format_type_be(INT4OID))));

    /* check that the type of the fourth column is TEXT if applicable */
    if (show_branch && TupleDescAttr(td, 3)->atttypid != TEXTOID)
        ereport(ERROR,
                (errcode(ERRCODE_DATATYPE_MISMATCH),
                 errmsg("invalid return type"),
                 errdetail("Fourth column must be type %s.",
                           format_type_be(TEXTOID))));

    /* check that the type of the fifth column is INT4 */
    if (show_branch && show_serial &&
        TupleDescAttr(td, 4)->atttypid != INT4OID)
        ereport(ERROR,
                (errcode(ERRCODE_DATATYPE_MISMATCH),
                 errmsg("query-specified return tuple not valid for Connectby: "
                        "fifth column must be type %s",
                        format_type_be(INT4OID))));

    /* check that the type of the fourth column is INT4 */
    if (!show_branch && show_serial &&
        TupleDescAttr(td, 3)->atttypid != INT4OID)
        ereport(ERROR,
                (errcode(ERRCODE_DATATYPE_MISMATCH),
                 errmsg("query-specified return tuple not valid for Connectby: "
                        "fourth column must be type %s",
                        format_type_be(INT4OID))));

    /* OK, the tupdesc is valid for our purposes */
}

/*
 * Check if spi sql tupdesc and return tupdesc are compatible
 */
static void
compatConnectbyTupleDescs(TupleDesc ret_tupdesc, TupleDesc sql_tupdesc)
{
    Oid         ret_atttypid;
    Oid         sql_atttypid;
    int32       ret_atttypmod;
    int32       sql_atttypmod;

    /*
     * Result must have at least 2 columns.
     */
    if (sql_tupdesc->natts < 2)
        ereport(ERROR,
                (errcode(ERRCODE_DATATYPE_MISMATCH),
                 errmsg("invalid return type"),
                 errdetail("Query must return at least two columns.")));

    /*
     * These columns must match the result type indicated by the calling
     * query.
     */
    ret_atttypid = TupleDescAttr(ret_tupdesc, 0)->atttypid;
    sql_atttypid = TupleDescAttr(sql_tupdesc, 0)->atttypid;
    ret_atttypmod = TupleDescAttr(ret_tupdesc, 0)->atttypmod;
    sql_atttypmod = TupleDescAttr(sql_tupdesc, 0)->atttypmod;
    if (ret_atttypid != sql_atttypid ||
        (ret_atttypmod >= 0 && ret_atttypmod != sql_atttypmod))
        ereport(ERROR,
                (errcode(ERRCODE_DATATYPE_MISMATCH),
                 errmsg("invalid return type"),
                 errdetail("SQL key field type %s does " \
                           "not match return key field type %s.",
                           format_type_with_typemod(ret_atttypid, ret_atttypmod),
                           format_type_with_typemod(sql_atttypid, sql_atttypmod))));

    ret_atttypid = TupleDescAttr(ret_tupdesc, 1)->atttypid;
    sql_atttypid = TupleDescAttr(sql_tupdesc, 1)->atttypid;
    ret_atttypmod = TupleDescAttr(ret_tupdesc, 1)->atttypmod;
    sql_atttypmod = TupleDescAttr(sql_tupdesc, 1)->atttypmod;
    if (ret_atttypid != sql_atttypid ||
        (ret_atttypmod >= 0 && ret_atttypmod != sql_atttypmod))
        ereport(ERROR,
                (errcode(ERRCODE_DATATYPE_MISMATCH),
                 errmsg("invalid return type"),
                 errdetail("SQL parent key field type %s does " \
                           "not match return parent key field type %s.",
                           format_type_with_typemod(ret_atttypid, ret_atttypmod),
                           format_type_with_typemod(sql_atttypid, sql_atttypmod))));

    /* OK, the two tupdescs are compatible for our purposes */
}

/*
 * Check if two tupdescs match in type of attributes
 */
static bool
compatCrosstabTupleDescs(TupleDesc ret_tupdesc, TupleDesc sql_tupdesc)
{
    int         i;
    Form_pg_attribute ret_attr;
    Oid         ret_atttypid;
    Form_pg_attribute sql_attr;
    Oid         sql_atttypid;

    if (ret_tupdesc->natts < 2 ||
        sql_tupdesc->natts < 3)
        return false;

    /* check the rowid types match */
    ret_atttypid = TupleDescAttr(ret_tupdesc, 0)->atttypid;
    sql_atttypid = TupleDescAttr(sql_tupdesc, 0)->atttypid;
    if (ret_atttypid != sql_atttypid)
        ereport(ERROR,
                (errcode(ERRCODE_DATATYPE_MISMATCH),
                 errmsg("invalid return type"),
                 errdetail("SQL rowid datatype does not match " \
                           "return rowid datatype.")));

    /*
     * - attribute [1] of the sql tuple is the category; no need to check it -
     * attribute [2] of the sql tuple should match attributes [1] to [natts]
     * of the return tuple
     */
    sql_attr = TupleDescAttr(sql_tupdesc, 2);
    for (i = 1; i < ret_tupdesc->natts; i++)
    {
        ret_attr = TupleDescAttr(ret_tupdesc, i);

        if (ret_attr->atttypid != sql_attr->atttypid)
            return false;
    }

    /* OK, the two tupdescs are compatible for our purposes */
    return true;
}