tupdesc.c

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/*-------------------------------------------------------------------------
 *
 * tupdesc.c
 *    POSTGRES tuple descriptor support code
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/access/common/tupdesc.c
 *
 * NOTES
 *    some of the executor utility code such as "ExecTypeFromTL" should be
 *    moved here.
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "access/htup_details.h"
#include "access/toast_compression.h"
#include "access/tupdesc_details.h"
#include "catalog/pg_collation.h"
#include "catalog/pg_type.h"
#include "common/hashfn.h"
#include "miscadmin.h"
#include "parser/parse_type.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/datum.h"
#include "utils/resowner_private.h"
#include "utils/syscache.h"
 
 
/*
 * CreateTemplateTupleDesc
 *      This function allocates an empty tuple descriptor structure.
 *
 * Tuple type ID information is initially set for an anonymous record type;
 * caller can overwrite this if needed.
 */
TupleDesc
CreateTemplateTupleDesc(int natts)
{
    TupleDesc   desc;
 
    /*
     * sanity checks
     */
    Assert(natts >= 0);
 
    /*
     * Allocate enough memory for the tuple descriptor, including the
     * attribute rows.
     *
     * Note: the attribute array stride is sizeof(FormData_pg_attribute),
     * since we declare the array elements as FormData_pg_attribute for
     * notational convenience.  However, we only guarantee that the first
     * ATTRIBUTE_FIXED_PART_SIZE bytes of each entry are valid; most code that
     * copies tupdesc entries around copies just that much.  In principle that
     * could be less due to trailing padding, although with the current
     * definition of pg_attribute there probably isn't any padding.
     */
    desc = (TupleDesc) palloc(offsetof(struct TupleDescData, attrs) +
                              natts * sizeof(FormData_pg_attribute));
 
    /*
     * Initialize other fields of the tupdesc.
     */
    desc->natts = natts;
    desc->constr = NULL;
    desc->tdtypeid = RECORDOID;
    desc->tdtypmod = -1;
    desc->tdrefcount = -1;      /* assume not reference-counted */
 
    return desc;
}
 
/*
 * CreateTupleDesc
 *      This function allocates a new TupleDesc by copying a given
 *      Form_pg_attribute array.
 *
 * Tuple type ID information is initially set for an anonymous record type;
 * caller can overwrite this if needed.
 */
TupleDesc
CreateTupleDesc(int natts, Form_pg_attribute *attrs)
{
    TupleDesc   desc;
    int         i;
 
    desc = CreateTemplateTupleDesc(natts);
 
    for (i = 0; i < natts; ++i)
        memcpy(TupleDescAttr(desc, i), attrs[i], ATTRIBUTE_FIXED_PART_SIZE);
 
    return desc;
}
 
/*
 * CreateTupleDescCopy
 *      This function creates a new TupleDesc by copying from an existing
 *      TupleDesc.
 *
 * !!! Constraints and defaults are not copied !!!
 */
TupleDesc
CreateTupleDescCopy(TupleDesc tupdesc)
{
    TupleDesc   desc;
    int         i;
 
    desc = CreateTemplateTupleDesc(tupdesc->natts);
 
    /* Flat-copy the attribute array */
    memcpy(TupleDescAttr(desc, 0),
           TupleDescAttr(tupdesc, 0),
           desc->natts * sizeof(FormData_pg_attribute));
 
    /*
     * Since we're not copying constraints and defaults, clear fields
     * associated with them.
     */
    for (i = 0; i < desc->natts; i++)
    {
        Form_pg_attribute att = TupleDescAttr(desc, i);
 
        att->attnotnull = false;
        att->atthasdef = false;
        att->atthasmissing = false;
        att->attidentity = '\0';
        att->attgenerated = '\0';
    }
 
    /* We can copy the tuple type identification, too */
    desc->tdtypeid = tupdesc->tdtypeid;
    desc->tdtypmod = tupdesc->tdtypmod;
 
    return desc;
}
 
/*
 * CreateTupleDescCopyConstr
 *      This function creates a new TupleDesc by copying from an existing
 *      TupleDesc (including its constraints and defaults).
 */
TupleDesc
CreateTupleDescCopyConstr(TupleDesc tupdesc)
{
    TupleDesc   desc;
    TupleConstr *constr = tupdesc->constr;
    int         i;
 
    desc = CreateTemplateTupleDesc(tupdesc->natts);
 
    /* Flat-copy the attribute array */
    memcpy(TupleDescAttr(desc, 0),
           TupleDescAttr(tupdesc, 0),
           desc->natts * sizeof(FormData_pg_attribute));
 
    /* Copy the TupleConstr data structure, if any */
    if (constr)
    {
        TupleConstr *cpy = (TupleConstr *) palloc0(sizeof(TupleConstr));
 
        cpy->has_not_null = constr->has_not_null;
        cpy->has_generated_stored = constr->has_generated_stored;
 
        if ((cpy->num_defval = constr->num_defval) > 0)
        {
            cpy->defval = (AttrDefault *) palloc(cpy->num_defval * sizeof(AttrDefault));
            memcpy(cpy->defval, constr->defval, cpy->num_defval * sizeof(AttrDefault));
            for (i = cpy->num_defval - 1; i >= 0; i--)
                cpy->defval[i].adbin = pstrdup(constr->defval[i].adbin);
        }
 
        if (constr->missing)
        {
            cpy->missing = (AttrMissing *) palloc(tupdesc->natts * sizeof(AttrMissing));
            memcpy(cpy->missing, constr->missing, tupdesc->natts * sizeof(AttrMissing));
            for (i = tupdesc->natts - 1; i >= 0; i--)
            {
                if (constr->missing[i].am_present)
                {
                    Form_pg_attribute attr = TupleDescAttr(tupdesc, i);
 
                    cpy->missing[i].am_value = datumCopy(constr->missing[i].am_value,
                                                         attr->attbyval,
                                                         attr->attlen);
                }
            }
        }
 
        if ((cpy->num_check = constr->num_check) > 0)
        {
            cpy->check = (ConstrCheck *) palloc(cpy->num_check * sizeof(ConstrCheck));
            memcpy(cpy->check, constr->check, cpy->num_check * sizeof(ConstrCheck));
            for (i = cpy->num_check - 1; i >= 0; i--)
            {
                cpy->check[i].ccname = pstrdup(constr->check[i].ccname);
                cpy->check[i].ccbin = pstrdup(constr->check[i].ccbin);
                cpy->check[i].ccvalid = constr->check[i].ccvalid;
                cpy->check[i].ccnoinherit = constr->check[i].ccnoinherit;
            }
        }
 
        desc->constr = cpy;
    }
 
    /* We can copy the tuple type identification, too */
    desc->tdtypeid = tupdesc->tdtypeid;
    desc->tdtypmod = tupdesc->tdtypmod;
 
    return desc;
}
 
/*
 * TupleDescCopy
 *      Copy a tuple descriptor into caller-supplied memory.
 *      The memory may be shared memory mapped at any address, and must
 *      be sufficient to hold TupleDescSize(src) bytes.
 *
 * !!! Constraints and defaults are not copied !!!
 */
void
TupleDescCopy(TupleDesc dst, TupleDesc src)
{
    int         i;
 
    /* Flat-copy the header and attribute array */
    memcpy(dst, src, TupleDescSize(src));
 
    /*
     * Since we're not copying constraints and defaults, clear fields
     * associated with them.
     */
    for (i = 0; i < dst->natts; i++)
    {
        Form_pg_attribute att = TupleDescAttr(dst, i);
 
        att->attnotnull = false;
        att->atthasdef = false;
        att->atthasmissing = false;
        att->attidentity = '\0';
        att->attgenerated = '\0';
    }
    dst->constr = NULL;
 
    /*
     * Also, assume the destination is not to be ref-counted.  (Copying the
     * source's refcount would be wrong in any case.)
     */
    dst->tdrefcount = -1;
}
 
/*
 * TupleDescCopyEntry
 *      This function copies a single attribute structure from one tuple
 *      descriptor to another.
 *
 * !!! Constraints and defaults are not copied !!!
 */
void
TupleDescCopyEntry(TupleDesc dst, AttrNumber dstAttno,
                   TupleDesc src, AttrNumber srcAttno)
{
    Form_pg_attribute dstAtt = TupleDescAttr(dst, dstAttno - 1);
    Form_pg_attribute srcAtt = TupleDescAttr(src, srcAttno - 1);
 
    /*
     * sanity checks
     */
    Assert(PointerIsValid(src));
    Assert(PointerIsValid(dst));
    Assert(srcAttno >= 1);
    Assert(srcAttno <= src->natts);
    Assert(dstAttno >= 1);
    Assert(dstAttno <= dst->natts);
 
    memcpy(dstAtt, srcAtt, ATTRIBUTE_FIXED_PART_SIZE);
 
    /*
     * Aside from updating the attno, we'd better reset attcacheoff.
     *
     * XXX Actually, to be entirely safe we'd need to reset the attcacheoff of
     * all following columns in dst as well.  Current usage scenarios don't
     * require that though, because all following columns will get initialized
     * by other uses of this function or TupleDescInitEntry.  So we cheat a
     * bit to avoid a useless O(N^2) penalty.
     */
    dstAtt->attnum = dstAttno;
    dstAtt->attcacheoff = -1;
 
    /* since we're not copying constraints or defaults, clear these */
    dstAtt->attnotnull = false;
    dstAtt->atthasdef = false;
    dstAtt->atthasmissing = false;
    dstAtt->attidentity = '\0';
    dstAtt->attgenerated = '\0';
}
 
/*
 * Free a TupleDesc including all substructure
 */
void
FreeTupleDesc(TupleDesc tupdesc)
{
    int         i;
 
    /*
     * Possibly this should assert tdrefcount == 0, to disallow explicit
     * freeing of un-refcounted tupdescs?
     */
    Assert(tupdesc->tdrefcount <= 0);
 
    if (tupdesc->constr)
    {
        if (tupdesc->constr->num_defval > 0)
        {
            AttrDefault *attrdef = tupdesc->constr->defval;
 
            for (i = tupdesc->constr->num_defval - 1; i >= 0; i--)
                pfree(attrdef[i].adbin);
            pfree(attrdef);
        }
        if (tupdesc->constr->missing)
        {
            AttrMissing *attrmiss = tupdesc->constr->missing;
 
            for (i = tupdesc->natts - 1; i >= 0; i--)
            {
                if (attrmiss[i].am_present
                    && !TupleDescAttr(tupdesc, i)->attbyval)
                    pfree(DatumGetPointer(attrmiss[i].am_value));
            }
            pfree(attrmiss);
        }
        if (tupdesc->constr->num_check > 0)
        {
            ConstrCheck *check = tupdesc->constr->check;
 
            for (i = tupdesc->constr->num_check - 1; i >= 0; i--)
            {
                pfree(check[i].ccname);
                pfree(check[i].ccbin);
            }
            pfree(check);
        }
        pfree(tupdesc->constr);
    }
 
    pfree(tupdesc);
}
 
/*
 * Increment the reference count of a tupdesc, and log the reference in
 * CurrentResourceOwner.
 *
 * Do not apply this to tupdescs that are not being refcounted.  (Use the
 * macro PinTupleDesc for tupdescs of uncertain status.)
 */
void
IncrTupleDescRefCount(TupleDesc tupdesc)
{
    Assert(tupdesc->tdrefcount >= 0);
 
    ResourceOwnerEnlargeTupleDescs(CurrentResourceOwner);
    tupdesc->tdrefcount++;
    ResourceOwnerRememberTupleDesc(CurrentResourceOwner, tupdesc);
}
 
/*
 * Decrement the reference count of a tupdesc, remove the corresponding
 * reference from CurrentResourceOwner, and free the tupdesc if no more
 * references remain.
 *
 * Do not apply this to tupdescs that are not being refcounted.  (Use the
 * macro ReleaseTupleDesc for tupdescs of uncertain status.)
 */
void
DecrTupleDescRefCount(TupleDesc tupdesc)
{
    Assert(tupdesc->tdrefcount > 0);
 
    ResourceOwnerForgetTupleDesc(CurrentResourceOwner, tupdesc);
    if (--tupdesc->tdrefcount == 0)
        FreeTupleDesc(tupdesc);
}
 
/*
 * Compare two TupleDesc structures for logical equality
 *
 * Note: we deliberately do not check the attrelid and tdtypmod fields.
 * This allows typcache.c to use this routine to see if a cached record type
 * matches a requested type, and is harmless for relcache.c's uses.
 * We don't compare tdrefcount, either.
 */
bool
equalTupleDescs(TupleDesc tupdesc1, TupleDesc tupdesc2)
{
    int         i,
                n;
 
    if (tupdesc1->natts != tupdesc2->natts)
        return false;
    if (tupdesc1->tdtypeid != tupdesc2->tdtypeid)
        return false;
 
    for (i = 0; i < tupdesc1->natts; i++)
    {
        Form_pg_attribute attr1 = TupleDescAttr(tupdesc1, i);
        Form_pg_attribute attr2 = TupleDescAttr(tupdesc2, i);
 
        /*
         * We do not need to check every single field here: we can disregard
         * attrelid and attnum (which were used to place the row in the attrs
         * array in the first place).  It might look like we could dispense
         * with checking attlen/attbyval/attalign, since these are derived
         * from atttypid; but in the case of dropped columns we must check
         * them (since atttypid will be zero for all dropped columns) and in
         * general it seems safer to check them always.
         *
         * attcacheoff must NOT be checked since it's possibly not set in both
         * copies.  We also intentionally ignore atthasmissing, since that's
         * not very relevant in tupdescs, which lack the attmissingval field.
         */
        if (strcmp(NameStr(attr1->attname), NameStr(attr2->attname)) != 0)
            return false;
        if (attr1->atttypid != attr2->atttypid)
            return false;
        if (attr1->attstattarget != attr2->attstattarget)
            return false;
        if (attr1->attlen != attr2->attlen)
            return false;
        if (attr1->attndims != attr2->attndims)
            return false;
        if (attr1->atttypmod != attr2->atttypmod)
            return false;
        if (attr1->attbyval != attr2->attbyval)
            return false;
        if (attr1->attalign != attr2->attalign)
            return false;
        if (attr1->attstorage != attr2->attstorage)
            return false;
        if (attr1->attcompression != attr2->attcompression)
            return false;
        if (attr1->attnotnull != attr2->attnotnull)
            return false;
        if (attr1->atthasdef != attr2->atthasdef)
            return false;
        if (attr1->attidentity != attr2->attidentity)
            return false;
        if (attr1->attgenerated != attr2->attgenerated)
            return false;
        if (attr1->attisdropped != attr2->attisdropped)
            return false;
        if (attr1->attislocal != attr2->attislocal)
            return false;
        if (attr1->attinhcount != attr2->attinhcount)
            return false;
        if (attr1->attcollation != attr2->attcollation)
            return false;
        /* variable-length fields are not even present... */
    }
 
    if (tupdesc1->constr != NULL)
    {
        TupleConstr *constr1 = tupdesc1->constr;
        TupleConstr *constr2 = tupdesc2->constr;
 
        if (constr2 == NULL)
            return false;
        if (constr1->has_not_null != constr2->has_not_null)
            return false;
        if (constr1->has_generated_stored != constr2->has_generated_stored)
            return false;
        n = constr1->num_defval;
        if (n != (int) constr2->num_defval)
            return false;
        /* We assume here that both AttrDefault arrays are in adnum order */
        for (i = 0; i < n; i++)
        {
            AttrDefault *defval1 = constr1->defval + i;
            AttrDefault *defval2 = constr2->defval + i;
 
            if (defval1->adnum != defval2->adnum)
                return false;
            if (strcmp(defval1->adbin, defval2->adbin) != 0)
                return false;
        }
        if (constr1->missing)
        {
            if (!constr2->missing)
                return false;
            for (i = 0; i < tupdesc1->natts; i++)
            {
                AttrMissing *missval1 = constr1->missing + i;
                AttrMissing *missval2 = constr2->missing + i;
 
                if (missval1->am_present != missval2->am_present)
                    return false;
                if (missval1->am_present)
                {
                    Form_pg_attribute missatt1 = TupleDescAttr(tupdesc1, i);
 
                    if (!datumIsEqual(missval1->am_value, missval2->am_value,
                                      missatt1->attbyval, missatt1->attlen))
                        return false;
                }
            }
        }
        else if (constr2->missing)
            return false;
        n = constr1->num_check;
        if (n != (int) constr2->num_check)
            return false;
 
        /*
         * Similarly, we rely here on the ConstrCheck entries being sorted by
         * name.  If there are duplicate names, the outcome of the comparison
         * is uncertain, but that should not happen.
         */
        for (i = 0; i < n; i++)
        {
            ConstrCheck *check1 = constr1->check + i;
            ConstrCheck *check2 = constr2->check + i;
 
            if (!(strcmp(check1->ccname, check2->ccname) == 0 &&
                  strcmp(check1->ccbin, check2->ccbin) == 0 &&
                  check1->ccvalid == check2->ccvalid &&
                  check1->ccnoinherit == check2->ccnoinherit))
                return false;
        }
    }
    else if (tupdesc2->constr != NULL)
        return false;
    return true;
}
 
/*
 * hashTupleDesc
 *      Compute a hash value for a tuple descriptor.
 *
 * If two tuple descriptors would be considered equal by equalTupleDescs()
 * then their hash value will be equal according to this function.
 *
 * Note that currently contents of constraint are not hashed - it'd be a bit
 * painful to do so, and conflicts just due to constraints are unlikely.
 */
uint32
hashTupleDesc(TupleDesc desc)
{
    uint32      s;
    int         i;
 
    s = hash_combine(0, hash_uint32(desc->natts));
    s = hash_combine(s, hash_uint32(desc->tdtypeid));
    for (i = 0; i < desc->natts; ++i)
        s = hash_combine(s, hash_uint32(TupleDescAttr(desc, i)->atttypid));
 
    return s;
}
 
/*
 * TupleDescInitEntry
 *      This function initializes a single attribute structure in
 *      a previously allocated tuple descriptor.
 *
 * If attributeName is NULL, the attname field is set to an empty string
 * (this is for cases where we don't know or need a name for the field).
 * Also, some callers use this function to change the datatype-related fields
 * in an existing tupdesc; they pass attributeName = NameStr(att->attname)
 * to indicate that the attname field shouldn't be modified.
 *
 * Note that attcollation is set to the default for the specified datatype.
 * If a nondefault collation is needed, insert it afterwards using
 * TupleDescInitEntryCollation.
 */
void
TupleDescInitEntry(TupleDesc desc,
                   AttrNumber attributeNumber,
                   const char *attributeName,
                   Oid oidtypeid,
                   int32 typmod,
                   int attdim)
{
    HeapTuple   tuple;
    Form_pg_type typeForm;
    Form_pg_attribute att;
 
    /*
     * sanity checks
     */
    Assert(PointerIsValid(desc));
    Assert(attributeNumber >= 1);
    Assert(attributeNumber <= desc->natts);
 
    /*
     * initialize the attribute fields
     */
    att = TupleDescAttr(desc, attributeNumber - 1);
 
    att->attrelid = 0;          /* dummy value */
 
    /*
     * Note: attributeName can be NULL, because the planner doesn't always
     * fill in valid resname values in targetlists, particularly for resjunk
     * attributes. Also, do nothing if caller wants to re-use the old attname.
     */
    if (attributeName == NULL)
        MemSet(NameStr(att->attname), 0, NAMEDATALEN);
    else if (attributeName != NameStr(att->attname))
        namestrcpy(&(att->attname), attributeName);
 
    att->attstattarget = -1;
    att->attcacheoff = -1;
    att->atttypmod = typmod;
 
    att->attnum = attributeNumber;
    att->attndims = attdim;
 
    att->attnotnull = false;
    att->atthasdef = false;
    att->atthasmissing = false;
    att->attidentity = '\0';
    att->attgenerated = '\0';
    att->attisdropped = false;
    att->attislocal = true;
    att->attinhcount = 0;
    /* variable-length fields are not present in tupledescs */
 
    tuple = SearchSysCache1(TYPEOID, ObjectIdGetDatum(oidtypeid));
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for type %u", oidtypeid);
    typeForm = (Form_pg_type) GETSTRUCT(tuple);
 
    att->atttypid = oidtypeid;
    att->attlen = typeForm->typlen;
    att->attbyval = typeForm->typbyval;
    att->attalign = typeForm->typalign;
    att->attstorage = typeForm->typstorage;
    att->attcompression = InvalidCompressionMethod;
    att->attcollation = typeForm->typcollation;
 
    ReleaseSysCache(tuple);
}
 
/*
 * TupleDescInitBuiltinEntry
 *      Initialize a tuple descriptor without catalog access.  Only
 *      a limited range of builtin types are supported.
 */
void
TupleDescInitBuiltinEntry(TupleDesc desc,
                          AttrNumber attributeNumber,
                          const char *attributeName,
                          Oid oidtypeid,
                          int32 typmod,
                          int attdim)
{
    Form_pg_attribute att;
 
    /* sanity checks */
    Assert(PointerIsValid(desc));
    Assert(attributeNumber >= 1);
    Assert(attributeNumber <= desc->natts);
 
    /* initialize the attribute fields */
    att = TupleDescAttr(desc, attributeNumber - 1);
    att->attrelid = 0;          /* dummy value */
 
    /* unlike TupleDescInitEntry, we require an attribute name */
    Assert(attributeName != NULL);
    namestrcpy(&(att->attname), attributeName);
 
    att->attstattarget = -1;
    att->attcacheoff = -1;
    att->atttypmod = typmod;
 
    att->attnum = attributeNumber;
    att->attndims = attdim;
 
    att->attnotnull = false;
    att->atthasdef = false;
    att->atthasmissing = false;
    att->attidentity = '\0';
    att->attgenerated = '\0';
    att->attisdropped = false;
    att->attislocal = true;
    att->attinhcount = 0;
    /* variable-length fields are not present in tupledescs */
 
    att->atttypid = oidtypeid;
 
    /*
     * Our goal here is to support just enough types to let basic builtin
     * commands work without catalog access - e.g. so that we can do certain
     * things even in processes that are not connected to a database.
     */
    switch (oidtypeid)
    {
        case TEXTOID:
        case TEXTARRAYOID:
            att->attlen = -1;
            att->attbyval = false;
            att->attalign = TYPALIGN_INT;
            att->attstorage = TYPSTORAGE_EXTENDED;
            att->attcompression = InvalidCompressionMethod;
            att->attcollation = DEFAULT_COLLATION_OID;
            break;
 
        case BOOLOID:
            att->attlen = 1;
            att->attbyval = true;
            att->attalign = TYPALIGN_CHAR;
            att->attstorage = TYPSTORAGE_PLAIN;
            att->attcompression = InvalidCompressionMethod;
            att->attcollation = InvalidOid;
            break;
 
        case INT4OID:
            att->attlen = 4;
            att->attbyval = true;
            att->attalign = TYPALIGN_INT;
            att->attstorage = TYPSTORAGE_PLAIN;
            att->attcompression = InvalidCompressionMethod;
            att->attcollation = InvalidOid;
            break;
 
        case INT8OID:
            att->attlen = 8;
            att->attbyval = FLOAT8PASSBYVAL;
            att->attalign = TYPALIGN_DOUBLE;
            att->attstorage = TYPSTORAGE_PLAIN;
            att->attcompression = InvalidCompressionMethod;
            att->attcollation = InvalidOid;
            break;
 
        case OIDOID:
            att->attlen = 4;
            att->attbyval = true;
            att->attalign = TYPALIGN_INT;
            att->attstorage = TYPSTORAGE_PLAIN;
            att->attcompression = InvalidCompressionMethod;
            att->attcollation = InvalidOid;
            break;
 
        default:
            elog(ERROR, "unsupported type %u", oidtypeid);
    }
}
 
/*
 * TupleDescInitEntryCollation
 *
 * Assign a nondefault collation to a previously initialized tuple descriptor
 * entry.
 */
void
TupleDescInitEntryCollation(TupleDesc desc,
                            AttrNumber attributeNumber,
                            Oid collationid)
{
    /*
     * sanity checks
     */
    Assert(PointerIsValid(desc));
    Assert(attributeNumber >= 1);
    Assert(attributeNumber <= desc->natts);
 
    TupleDescAttr(desc, attributeNumber - 1)->attcollation = collationid;
}
 
 
/*
 * BuildDescForRelation
 *
 * Given a relation schema (list of ColumnDef nodes), build a TupleDesc.
 *
 * Note: tdtypeid will need to be filled in later on.
 */
TupleDesc
BuildDescForRelation(List *schema)
{
    int         natts;
    AttrNumber  attnum;
    ListCell   *l;
    TupleDesc   desc;
    bool        has_not_null;
    char       *attname;
    Oid         atttypid;
    int32       atttypmod;
    Oid         attcollation;
    int         attdim;
 
    /*
     * allocate a new tuple descriptor
     */
    natts = list_length(schema);
    desc = CreateTemplateTupleDesc(natts);
    has_not_null = false;
 
    attnum = 0;
 
    foreach(l, schema)
    {
        ColumnDef  *entry = lfirst(l);
        AclResult   aclresult;
        Form_pg_attribute att;
 
        /*
         * for each entry in the list, get the name and type information from
         * the list and have TupleDescInitEntry fill in the attribute
         * information we need.
         */
        attnum++;
 
        attname = entry->colname;
        typenameTypeIdAndMod(NULL, entry->typeName, &atttypid, &atttypmod);
 
        aclresult = object_aclcheck(TypeRelationId, atttypid, GetUserId(), ACL_USAGE);
        if (aclresult != ACLCHECK_OK)
            aclcheck_error_type(aclresult, atttypid);
 
        attcollation = GetColumnDefCollation(NULL, entry, atttypid);
        attdim = list_length(entry->typeName->arrayBounds);
 
        if (entry->typeName->setof)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                     errmsg("column \"%s\" cannot be declared SETOF",
                            attname)));
 
        TupleDescInitEntry(desc, attnum, attname,
                           atttypid, atttypmod, attdim);
        att = TupleDescAttr(desc, attnum - 1);
 
        /* Override TupleDescInitEntry's settings as requested */
        TupleDescInitEntryCollation(desc, attnum, attcollation);
        if (entry->storage)
            att->attstorage = entry->storage;
 
        /* Fill in additional stuff not handled by TupleDescInitEntry */
        att->attnotnull = entry->is_not_null;
        has_not_null |= entry->is_not_null;
        att->attislocal = entry->is_local;
        att->attinhcount = entry->inhcount;
    }
 
    if (has_not_null)
    {
        TupleConstr *constr = (TupleConstr *) palloc0(sizeof(TupleConstr));
 
        constr->has_not_null = true;
        constr->has_generated_stored = false;
        constr->defval = NULL;
        constr->missing = NULL;
        constr->num_defval = 0;
        constr->check = NULL;
        constr->num_check = 0;
        desc->constr = constr;
    }
    else
    {
        desc->constr = NULL;
    }
 
    return desc;
}
 
/*
 * BuildDescFromLists
 *
 * Build a TupleDesc given lists of column names (as String nodes),
 * column type OIDs, typmods, and collation OIDs.
 *
 * No constraints are generated.
 *
 * This is essentially a cut-down version of BuildDescForRelation for use
 * with functions returning RECORD.
 */
TupleDesc
BuildDescFromLists(List *names, List *types, List *typmods, List *collations)
{
    int         natts;
    AttrNumber  attnum;
    ListCell   *l1;
    ListCell   *l2;
    ListCell   *l3;
    ListCell   *l4;
    TupleDesc   desc;
 
    natts = list_length(names);
    Assert(natts == list_length(types));
    Assert(natts == list_length(typmods));
    Assert(natts == list_length(collations));
 
    /*
     * allocate a new tuple descriptor
     */
    desc = CreateTemplateTupleDesc(natts);
 
    attnum = 0;
    forfour(l1, names, l2, types, l3, typmods, l4, collations)
    {
        char       *attname = strVal(lfirst(l1));
        Oid         atttypid = lfirst_oid(l2);
        int32       atttypmod = lfirst_int(l3);
        Oid         attcollation = lfirst_oid(l4);
 
        attnum++;
 
        TupleDescInitEntry(desc, attnum, attname, atttypid, atttypmod, 0);
        TupleDescInitEntryCollation(desc, attnum, attcollation);
    }
 
    return desc;
}