rewriteGraphTable.c

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/*-------------------------------------------------------------------------
 *
 * rewriteGraphTable.c
 *      Support for rewriting GRAPH_TABLE clauses.
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/rewrite/rewriteGraphTable.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "access/genam.h"
#include "access/sysattr.h"
#include "access/table.h"
#include "access/htup_details.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_propgraph_element.h"
#include "catalog/pg_propgraph_element_label.h"
#include "catalog/pg_propgraph_label.h"
#include "catalog/pg_propgraph_label_property.h"
#include "catalog/pg_propgraph_property.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/optimizer.h"
#include "parser/analyze.h"
#include "parser/parse_collate.h"
#include "parser/parse_func.h"
#include "parser/parse_node.h"
#include "parser/parse_oper.h"
#include "parser/parse_relation.h"
#include "parser/parsetree.h"
#include "parser/parse_graphtable.h"
#include "rewrite/rewriteGraphTable.h"
#include "rewrite/rewriteHandler.h"
#include "rewrite/rewriteManip.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/lsyscache.h"
#include "utils/ruleutils.h"
#include "utils/syscache.h"
 
 
/*
 * Represents one path factor in a path.
 *
 * In a non-cyclic path, one path factor corresponds to one element pattern.
 *
 * In a cyclic path, one path factor corresponds to all the element patterns with
 * the same variable name.
 */
struct path_factor
{
    GraphElementPatternKind kind;
    const char *variable;
    Node       *labelexpr;
    Node       *whereClause;
    int         factorpos;      /* Position of this path factor in the list of
                                 * path factors representing a given path
                                 * pattern. */
    List       *labeloids;      /* OIDs of all the labels referenced in
                                 * labelexpr. */
    /* Links to adjacent vertex path factors if this is an edge path factor. */
    struct path_factor *src_pf;
    struct path_factor *dest_pf;
};
 
/*
 * Represents one property graph element (vertex or edge) in the path.
 *
 * Label expression in an element pattern resolves into a set of elements. We
 * create one path_element object for each of those elements.
 */
struct path_element
{
    /* Path factor from which this element is derived. */
    struct path_factor *path_factor;
    Oid         elemoid;
    Oid         reloid;
    /* Source and destination vertex elements for an edge element. */
    Oid         srcvertexid;
    Oid         destvertexid;
    /* Source and destination conditions for an edge element. */
    List       *src_quals;
    List       *dest_quals;
};
 
static Node *replace_property_refs(Oid propgraphid, Node *node, const List *mappings);
static List *build_edge_vertex_link_quals(HeapTuple edgetup, int edgerti, int refrti, Oid refid, AttrNumber catalog_key_attnum, AttrNumber catalog_ref_attnum, AttrNumber catalog_eqop_attnum);
static List *generate_queries_for_path_pattern(RangeTblEntry *rte, List *element_patterns);
static Query *generate_query_for_graph_path(RangeTblEntry *rte, List *path);
static Node *generate_setop_from_pathqueries(List *pathqueries, List **rtable, List **targetlist);
static List *generate_queries_for_path_pattern_recurse(RangeTblEntry *rte, List *pathqueries, List *cur_path, List *path_pattern_lists, int elempos);
static Query *generate_query_for_empty_path_pattern(RangeTblEntry *rte);
static Query *generate_union_from_pathqueries(List **pathqueries);
static List *get_path_elements_for_path_factor(Oid propgraphid, struct path_factor *pf);
static bool is_property_associated_with_label(Oid labeloid, Oid propoid);
static Node *get_element_property_expr(Oid elemoid, Oid propoid, int rtindex);
 
/*
 * Convert GRAPH_TABLE clause into a subquery using relational
 * operators.
 */
Query *
rewriteGraphTable(Query *parsetree, int rt_index)
{
    RangeTblEntry *rte;
    Query      *graph_table_query;
    List       *path_pattern;
    List       *pathqueries = NIL;
 
    rte = rt_fetch(rt_index, parsetree->rtable);
 
    Assert(list_length(rte->graph_pattern->path_pattern_list) == 1);
 
    path_pattern = linitial(rte->graph_pattern->path_pattern_list);
    pathqueries = generate_queries_for_path_pattern(rte, path_pattern);
    graph_table_query = generate_union_from_pathqueries(&pathqueries);
 
    AcquireRewriteLocks(graph_table_query, true, false);
 
    rte->rtekind = RTE_SUBQUERY;
    rte->subquery = graph_table_query;
    rte->lateral = true;
 
    /*
     * Reset no longer applicable fields, to appease
     * WRITE_READ_PARSE_PLAN_TREES.
     */
    rte->graph_pattern = NULL;
    rte->graph_table_columns = NIL;
 
    return parsetree;
}
 
/*
 * Generate queries representing the given path pattern applied to the given
 * property graph.
 *
 * A path pattern consists of one or more element patterns. Each of the element
 * patterns may be satisfied by multiple elements. A path satisfying the given
 * path pattern consists of one element from each element pattern.  There can be
 * as many paths as the number of combinations of the elements.  A path pattern
 * in itself is a K-partite graph where K = number of element patterns in the
 * path pattern. The possible paths are computed by performing a DFS in this
 * graph. The DFS is implemented as recursion. Each of these paths is converted
 * into a query connecting all the elements in that path. Set of these queries is
 * returned.
 *
 * Between every two vertex elements in the path there is an edge element that
 * connects them.  An edge connects two vertexes identified by the source and
 * destination keys respectively. The connection between an edge and its
 * adjacent vertex is naturally computed as an equi-join between edge and vertex
 * table on their respective keys. Hence the query representing one path
 * consists of JOINs between edge and vertex tables.
 *
 * generate_queries_for_path_pattern() starts the recursion but actual work is
 * done by generate_queries_for_path_pattern_recurse().
 * generate_query_for_graph_path() constructs a query for a given path.
 *
 * A path pattern may result into no path if any of the element pattern yields no
 * elements or edge patterns yield no edges connecting adjacent vertex patterns.
 * In such a case a dummy query which returns no result is returned
 * (generate_query_for_empty_path_pattern()).
 *
 * 'path_pattern' is given path pattern to be applied on the property graph in
 * the GRAPH_TABLE clause represented by given 'rte'.
 */
static List *
generate_queries_for_path_pattern(RangeTblEntry *rte, List *path_pattern)
{
    List       *pathqueries = NIL;
    List       *path_elem_lists = NIL;
    int         factorpos = 0;
    List       *path_factors = NIL;
    struct path_factor *prev_pf = NULL;
 
    Assert(list_length(path_pattern) > 0);
 
    /*
     * Create a list of path factors representing the given path pattern
     * linking edge path factors to their adjacent vertex path factors.
     *
     * While doing that merge element patterns with the same variable name
     * into a single path_factor.
     */
    foreach_node(GraphElementPattern, gep, path_pattern)
    {
        struct path_factor *pf = NULL;
 
        /*
         * Unsupported conditions should have been caught by the parser
         * itself. We have corresponding Asserts here to document the
         * assumptions in this code.
         */
        Assert(gep->kind == VERTEX_PATTERN || IS_EDGE_PATTERN(gep->kind));
        Assert(!gep->quantifier);
 
        foreach_ptr(struct path_factor, other, path_factors)
        {
            if (gep->variable && other->variable &&
                strcmp(gep->variable, other->variable) == 0)
            {
                if (other->kind != gep->kind)
                    ereport(ERROR,
                            (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                             errmsg("element patterns with same variable name \"%s\" but different element pattern types",
                                    gep->variable)));
 
                /*
                 * If both the element patterns have label expressions, they
                 * need to be conjuncted, which is not supported right now.
                 *
                 * However, an empty label expression means all labels.
                 * Conjunction of any label expression with all labels is the
                 * expression itself. Hence if only one of the two element
                 * patterns has a label expression use that expression.
                 */
                if (!other->labelexpr)
                    other->labelexpr = gep->labelexpr;
                else if (gep->labelexpr && !equal(other->labelexpr, gep->labelexpr))
                    ereport(ERROR,
                            (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                             errmsg("element patterns with same variable name \"%s\" but different label expressions are not supported",
                                    gep->variable)));
 
                /*
                 * If two element patterns have the same variable name, they
                 * represent the same set of graph elements and hence are
                 * constrained by conditions from both the element patterns.
                 */
                if (!other->whereClause)
                    other->whereClause = gep->whereClause;
                else if (gep->whereClause)
                    other->whereClause = (Node *) makeBoolExpr(AND_EXPR,
                                                               list_make2(other->whereClause, gep->whereClause),
                                                               -1);
                pf = other;
                break;
            }
        }
 
        if (!pf)
        {
            pf = palloc0_object(struct path_factor);
            pf->factorpos = factorpos++;
            pf->kind = gep->kind;
            pf->labelexpr = gep->labelexpr;
            pf->variable = gep->variable;
            pf->whereClause = gep->whereClause;
 
            path_factors = lappend(path_factors, pf);
        }
 
        /*
         * Setup links to the previous path factor in the path.
         *
         * If the previous path factor represents an edge, this path factor
         * represents an adjacent vertex; the source vertex for an edge
         * pointing left or the destination vertex for an edge pointing right.
         * If this path factor represents an edge, the previous path factor
         * represents an adjacent vertex; source vertex for an edge pointing
         * right or the destination vertex for an edge pointing left.
         *
         * Edge pointing in any direction is treated similar to that pointing
         * in right direction here.  When constructing a query in
         * generate_query_for_graph_path(), we will try links in both the
         * directions.
         *
         * If multiple edge patterns share the same variable name, they
         * constrain the adjacent vertex patterns since an edge can connect
         * only one pair of vertexes. These adjacent vertex patterns need to
         * be merged even though they have different variables. Such element
         * patterns form a walk of graph where vertex and edges are repeated.
         * For example, in (a)-[b]->(c)<-[b]-(d), (a) and (d) represent the
         * same vertex element. This is slightly harder to implement and
         * probably less useful. Hence not supported for now.
         */
        if (prev_pf)
        {
            if (prev_pf->kind == EDGE_PATTERN_RIGHT || prev_pf->kind == EDGE_PATTERN_ANY)
            {
                Assert(!IS_EDGE_PATTERN(pf->kind));
                if (prev_pf->dest_pf && prev_pf->dest_pf != pf)
                    ereport(ERROR,
                            errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                            errmsg("an edge cannot connect more than two vertexes even in a cyclic pattern"));
                prev_pf->dest_pf = pf;
            }
            else if (prev_pf->kind == EDGE_PATTERN_LEFT)
            {
                Assert(!IS_EDGE_PATTERN(pf->kind));
                if (prev_pf->src_pf && prev_pf->src_pf != pf)
                    ereport(ERROR,
                            errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                            errmsg("an edge cannot connect more than two vertexes even in a cyclic pattern"));
                prev_pf->src_pf = pf;
            }
            else
            {
                Assert(prev_pf->kind == VERTEX_PATTERN);
                Assert(IS_EDGE_PATTERN(pf->kind));
            }
 
            if (pf->kind == EDGE_PATTERN_RIGHT || pf->kind == EDGE_PATTERN_ANY)
            {
                Assert(!IS_EDGE_PATTERN(prev_pf->kind));
                if (pf->src_pf && pf->src_pf != prev_pf)
                    ereport(ERROR,
                            errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                            errmsg("an edge cannot connect more than two vertexes even in a cyclic pattern"));
                pf->src_pf = prev_pf;
            }
            else if (pf->kind == EDGE_PATTERN_LEFT)
            {
                Assert(!IS_EDGE_PATTERN(prev_pf->kind));
                if (pf->dest_pf && pf->dest_pf != prev_pf)
                    ereport(ERROR,
                            errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                            errmsg("an edge cannot connect more than two vertexes even in a cyclic pattern"));
                pf->dest_pf = prev_pf;
            }
            else
            {
                Assert(pf->kind == VERTEX_PATTERN);
                Assert(IS_EDGE_PATTERN(prev_pf->kind));
            }
        }
 
        prev_pf = pf;
    }
 
    /*
     * Collect list of elements for each path factor. Do this after all the
     * edge links are setup correctly.
     */
    foreach_ptr(struct path_factor, pf, path_factors)
        path_elem_lists = lappend(path_elem_lists,
                                  get_path_elements_for_path_factor(rte->relid, pf));
 
    pathqueries = generate_queries_for_path_pattern_recurse(rte, pathqueries,
                                                            NIL, path_elem_lists, 0);
    if (!pathqueries)
        pathqueries = list_make1(generate_query_for_empty_path_pattern(rte));
 
    return pathqueries;
}
 
/*
 * Recursive workhorse function of generate_queries_for_path_pattern().
 *
 * `elempos` is the position of the next element being added in the path being
 * built.
 */
static List *
generate_queries_for_path_pattern_recurse(RangeTblEntry *rte, List *pathqueries, List *cur_path, List *path_elem_lists, int elempos)
{
    List       *path_elems = list_nth_node(List, path_elem_lists, elempos);
 
    foreach_ptr(struct path_element, pe, path_elems)
    {
        /* Update current path being built with current element. */
        cur_path = lappend(cur_path, pe);
 
        /*
         * If this is the last element in the path, generate query for the
         * completed path. Else recurse processing the next element.
         */
        if (list_length(path_elem_lists) == list_length(cur_path))
        {
            Query      *pathquery = generate_query_for_graph_path(rte, cur_path);
 
            Assert(elempos == list_length(path_elem_lists) - 1);
            if (pathquery)
                pathqueries = lappend(pathqueries, pathquery);
        }
        else
            pathqueries = generate_queries_for_path_pattern_recurse(rte, pathqueries,
                                                                    cur_path,
                                                                    path_elem_lists,
                                                                    elempos + 1);
        /* Make way for the next element at the same position. */
        cur_path = list_delete_last(cur_path);
    }
 
    return pathqueries;
}
 
/*
 * Construct a query representing given graph path.
 *
 * The query contains:
 *
 * 1. targetlist corresponding to the COLUMNS clause of GRAPH_TABLE clause
 *
 * 2. quals corresponding to the WHERE clause of individual elements, WHERE
 * clause in GRAPH_TABLE clause and quals representing edge-vertex links.
 *
 * 3. fromlist containing all elements in the path
 *
 * The collations of property expressions are obtained from the catalog. The
 * collations of expressions in COLUMNS and WHERE clauses are assigned before
 * rewriting the graph table.  The collations of the edge-vertex link quals are
 * assigned when crafting those quals. Thus everything in the query that requires
 * collation assignment has been taken care of already. No separate collation
 * assignment is required in this function.
 *
 * More details in the prologue of generate_queries_for_path_pattern().
 */
static Query *
generate_query_for_graph_path(RangeTblEntry *rte, List *graph_path)
{
    Query      *path_query = makeNode(Query);
    List       *fromlist = NIL;
    List       *qual_exprs = NIL;
    List       *vars;
 
    path_query->commandType = CMD_SELECT;
 
    foreach_ptr(struct path_element, pe, graph_path)
    {
        struct path_factor *pf = pe->path_factor;
        RangeTblRef *rtr;
        Relation    rel;
        ParseNamespaceItem *pni;
 
        Assert(pf->kind == VERTEX_PATTERN || IS_EDGE_PATTERN(pf->kind));
 
        /* Add conditions representing edge connections. */
        if (IS_EDGE_PATTERN(pf->kind))
        {
            struct path_element *src_pe;
            struct path_element *dest_pe;
            Expr       *edge_qual = NULL;
 
            Assert(pf->src_pf && pf->dest_pf);
            src_pe = list_nth(graph_path, pf->src_pf->factorpos);
            dest_pe = list_nth(graph_path, pf->dest_pf->factorpos);
 
            /* Make sure that the links of adjacent vertices are correct. */
            Assert(pf->src_pf == src_pe->path_factor &&
                   pf->dest_pf == dest_pe->path_factor);
 
            if (src_pe->elemoid == pe->srcvertexid &&
                dest_pe->elemoid == pe->destvertexid)
                edge_qual = makeBoolExpr(AND_EXPR,
                                         list_concat(copyObject(pe->src_quals),
                                                     copyObject(pe->dest_quals)),
                                         -1);
 
            /*
             * An edge pattern in any direction matches edges in both
             * directions, try swapping source and destination. When the
             * source and destination is the same vertex table, quals
             * corresponding to either direction may get satisfied. Hence OR
             * the quals corresponding to both the directions.
             */
            if (pf->kind == EDGE_PATTERN_ANY &&
                dest_pe->elemoid == pe->srcvertexid &&
                src_pe->elemoid == pe->destvertexid)
            {
                List       *src_quals = copyObject(pe->dest_quals);
                List       *dest_quals = copyObject(pe->src_quals);
                Expr       *rev_edge_qual;
 
                /* Swap the source and destination varnos in the quals. */
                ChangeVarNodes((Node *) dest_quals, pe->path_factor->src_pf->factorpos + 1,
                               pe->path_factor->dest_pf->factorpos + 1, 0);
                ChangeVarNodes((Node *) src_quals, pe->path_factor->dest_pf->factorpos + 1,
                               pe->path_factor->src_pf->factorpos + 1, 0);
 
                rev_edge_qual = makeBoolExpr(AND_EXPR, list_concat(src_quals, dest_quals), -1);
                if (edge_qual)
                    edge_qual = makeBoolExpr(OR_EXPR, list_make2(edge_qual, rev_edge_qual), -1);
                else
                    edge_qual = rev_edge_qual;
            }
 
            /*
             * If the given edge element does not connect the adjacent vertex
             * elements in this path, the path is broken. Abandon this path as
             * it won't return any rows.
             */
            if (edge_qual == NULL)
                return NULL;
 
            qual_exprs = lappend(qual_exprs, edge_qual);
        }
        else
            Assert(!pe->src_quals && !pe->dest_quals);
 
        /*
         * Create RangeTblEntry for this element table.
         *
         * SQL/PGQ standard (Ref. Section 11.19, Access rule 2 and General
         * rule 4) does not specify whose access privileges to use when
         * accessing the element tables: property graph owner's or current
         * user's. It is safer to use current user's privileges so as not to
         * make property graphs as a hole for unpriviledged data access. This
         * is inline with the views being security_invoker by default.
         */
        rel = table_open(pe->reloid, AccessShareLock);
        pni = addRangeTableEntryForRelation(make_parsestate(NULL), rel, AccessShareLock,
                                            NULL, true, false);
        table_close(rel, NoLock);
        path_query->rtable = lappend(path_query->rtable, pni->p_rte);
        path_query->rteperminfos = lappend(path_query->rteperminfos, pni->p_perminfo);
        pni->p_rte->perminfoindex = list_length(path_query->rteperminfos);
        rtr = makeNode(RangeTblRef);
        rtr->rtindex = list_length(path_query->rtable);
        fromlist = lappend(fromlist, rtr);
 
        /*
         * Make sure that the assumption mentioned in create_pe_for_element()
         * holds true; that the elements' RangeTblEntrys are added in the
         * order in which their respective path factors appear in the list of
         * path factors representing the path pattern.
         */
        Assert(pf->factorpos + 1 == rtr->rtindex);
 
        if (pf->whereClause)
        {
            Node       *tr;
 
            tr = replace_property_refs(rte->relid, pf->whereClause, list_make1(pe));
 
            qual_exprs = lappend(qual_exprs, tr);
        }
    }
 
    if (rte->graph_pattern->whereClause)
    {
        Node       *path_quals = replace_property_refs(rte->relid,
                                                       (Node *) rte->graph_pattern->whereClause,
                                                       graph_path);
 
        qual_exprs = lappend(qual_exprs, path_quals);
    }
 
    path_query->jointree = makeFromExpr(fromlist,
                                        qual_exprs ? (Node *) makeBoolExpr(AND_EXPR, qual_exprs, -1) : NULL);
 
    /* Construct query targetlist from COLUMNS specification of GRAPH_TABLE. */
    path_query->targetList = castNode(List,
                                      replace_property_refs(rte->relid,
                                                            (Node *) rte->graph_table_columns,
                                                            graph_path));
 
    /*
     * Mark the columns being accessed in the path query as requiring SELECT
     * privilege. Any lateral columns should have been handled when the
     * corresponding ColumnRefs were transformed. Ignore those here.
     */
    vars = pull_vars_of_level((Node *) list_make2(qual_exprs, path_query->targetList), 0);
    foreach_node(Var, var, vars)
    {
        RTEPermissionInfo *perminfo = getRTEPermissionInfo(path_query->rteperminfos,
                                                           rt_fetch(var->varno, path_query->rtable));
 
        /* Must offset the attnum to fit in a bitmapset */
        perminfo->selectedCols = bms_add_member(perminfo->selectedCols,
                                                var->varattno - FirstLowInvalidHeapAttributeNumber);
    }
 
    return path_query;
}
 
/*
 * Construct a query which would not return any rows.
 *
 * More details in the prologue of generate_queries_for_path_pattern().
 */
static Query *
generate_query_for_empty_path_pattern(RangeTblEntry *rte)
{
    Query      *query = makeNode(Query);
 
    query->commandType = CMD_SELECT;
    query->rtable = NIL;
    query->rteperminfos = NIL;
    query->jointree = makeFromExpr(NIL, (Node *) makeBoolConst(false, false));
 
    /*
     * Even though no rows are returned, the result still projects the same
     * columns as projected by GRAPH_TABLE clause. Do this by constructing a
     * target list full of NULL values.
     */
    foreach_node(TargetEntry, te, rte->graph_table_columns)
    {
        Node       *nte = (Node *) te->expr;
 
        te->expr = (Expr *) makeNullConst(exprType(nte), exprTypmod(nte), exprCollation(nte));
        query->targetList = lappend(query->targetList, te);
    }
 
    return query;
}
 
/*
 * Construct a query which is UNION of given path queries.
 *
 * The UNION query derives collations of its targetlist entries from the
 * corresponding targetlist entries of the path queries. The targetlists of path
 * queries being UNION'ed already have collations assigned.  No separate
 * collation assignment required in this function.
 *
 * The function destroys given pathqueries list while constructing
 * SetOperationStmt recursively. Hence the function always returns with
 * `pathqueries` set to NIL.
 */
static Query *
generate_union_from_pathqueries(List **pathqueries)
{
    List       *rtable = NIL;
    Query      *sampleQuery = linitial_node(Query, *pathqueries);
    SetOperationStmt *sostmt;
    Query      *union_query;
    int         resno;
    ListCell   *lctl,
               *lct,
               *lcm,
               *lcc;
 
    Assert(list_length(*pathqueries) > 0);
 
    /* If there's only one pathquery, no need to construct a UNION query. */
    if (list_length(*pathqueries) == 1)
    {
        *pathqueries = NIL;
        return sampleQuery;
    }
 
    sostmt = castNode(SetOperationStmt,
                      generate_setop_from_pathqueries(*pathqueries, &rtable, NULL));
 
    /* Encapsulate the set operation statement into a Query. */
    union_query = makeNode(Query);
    union_query->commandType = CMD_SELECT;
    union_query->rtable = rtable;
    union_query->setOperations = (Node *) sostmt;
    union_query->rteperminfos = NIL;
    union_query->jointree = makeFromExpr(NIL, NULL);
 
    /*
     * Generate dummy targetlist for outer query using column names from one
     * of the queries and common datatypes/collations of topmost set
     * operation.  It shouldn't matter which query. Also it shouldn't matter
     * which RT index is used as varno in the target list entries, as long as
     * it corresponds to a real RT entry; else funny things may happen when
     * the tree is mashed by rule rewriting. So we use 1 since there's always
     * one RT entry at least.
     */
    Assert(rt_fetch(1, rtable));
    union_query->targetList = NULL;
    resno = 1;
    forfour(lct, sostmt->colTypes,
            lcm, sostmt->colTypmods,
            lcc, sostmt->colCollations,
            lctl, sampleQuery->targetList)
    {
        Oid         colType = lfirst_oid(lct);
        int32       colTypmod = lfirst_int(lcm);
        Oid         colCollation = lfirst_oid(lcc);
        TargetEntry *sample_tle = (TargetEntry *) lfirst(lctl);
        char       *colName;
        TargetEntry *tle;
        Var        *var;
 
        Assert(!sample_tle->resjunk);
        colName = pstrdup(sample_tle->resname);
        var = makeVar(1, sample_tle->resno, colType, colTypmod, colCollation, 0);
        var->location = exprLocation((Node *) sample_tle->expr);
        tle = makeTargetEntry((Expr *) var, (AttrNumber) resno++, colName, false);
        union_query->targetList = lappend(union_query->targetList, tle);
    }
 
    *pathqueries = NIL;
    return union_query;
}
 
/*
 * Construct a query which is UNION of all the given path queries.
 *
 * The function destroys given pathqueries list while constructing
 * SetOperationStmt recursively.
 */
static Node *
generate_setop_from_pathqueries(List *pathqueries, List **rtable, List **targetlist)
{
    SetOperationStmt *sostmt;
    Query      *lquery;
    Node       *rarg;
    RangeTblRef *lrtr = makeNode(RangeTblRef);
    List       *rtargetlist;
    ParseNamespaceItem *pni;
 
    /* Recursion termination condition. */
    if (list_length(pathqueries) == 0)
    {
        *targetlist = NIL;
        return NULL;
    }
 
    lquery = linitial_node(Query, pathqueries);
 
    pni = addRangeTableEntryForSubquery(make_parsestate(NULL), lquery, NULL,
                                        false, false);
    *rtable = lappend(*rtable, pni->p_rte);
    lrtr->rtindex = list_length(*rtable);
    rarg = generate_setop_from_pathqueries(list_delete_first(pathqueries), rtable, &rtargetlist);
    if (rarg == NULL)
    {
        /*
         * No further path queries in the list. Convert the last query into a
         * RangeTblRef as expected by SetOperationStmt. Extract a list of the
         * non-junk TLEs for upper-level processing.
         */
        if (targetlist)
        {
            *targetlist = NIL;
            foreach_node(TargetEntry, tle, lquery->targetList)
            {
                if (!tle->resjunk)
                    *targetlist = lappend(*targetlist, tle);
            }
        }
        return (Node *) lrtr;
    }
 
    sostmt = makeNode(SetOperationStmt);
    sostmt->op = SETOP_UNION;
    sostmt->all = true;
    sostmt->larg = (Node *) lrtr;
    sostmt->rarg = rarg;
    constructSetOpTargetlist(NULL, sostmt, lquery->targetList, rtargetlist, targetlist, "UNION", false);
 
    return (Node *) sostmt;
}
 
/*
 * Construct a path_element object for the graph element given by `elemoid`
 * satisfied by the path factor `pf`.
 *
 * If the type of graph element does not fit the element pattern kind, the
 * function returns NULL.
 */
static struct path_element *
create_pe_for_element(struct path_factor *pf, Oid elemoid)
{
    HeapTuple   eletup = SearchSysCache1(PROPGRAPHELOID, ObjectIdGetDatum(elemoid));
    Form_pg_propgraph_element pgeform;
    struct path_element *pe;
 
    if (!eletup)
        elog(ERROR, "cache lookup failed for property graph element %u", elemoid);
    pgeform = ((Form_pg_propgraph_element) GETSTRUCT(eletup));
 
    if ((pgeform->pgekind == PGEKIND_VERTEX && pf->kind != VERTEX_PATTERN) ||
        (pgeform->pgekind == PGEKIND_EDGE && !IS_EDGE_PATTERN(pf->kind)))
    {
        ReleaseSysCache(eletup);
        return NULL;
    }
 
    pe = palloc0_object(struct path_element);
    pe->path_factor = pf;
    pe->elemoid = elemoid;
    pe->reloid = pgeform->pgerelid;
 
    /*
     * When a path is converted into a query
     * (generate_query_for_graph_path()), a RangeTblEntry will be created for
     * every element in the path.  Fixing rtindexes of RangeTblEntrys here
     * makes it possible to craft elements' qual expressions only once while
     * we have access to the catalog entry. Otherwise they need to be crafted
     * as many times as the number of paths a given element appears in,
     * fetching catalog entry again each time.  Hence we simply assume
     * RangeTblEntrys will be created in the same order in which the
     * corresponding path factors appear in the list of path factors
     * representing a path pattern. That way their rtindexes will be same as
     * path_factor::factorpos + 1.
     */
    if (IS_EDGE_PATTERN(pf->kind))
    {
        pe->srcvertexid = pgeform->pgesrcvertexid;
        pe->destvertexid = pgeform->pgedestvertexid;
        Assert(pf->src_pf && pf->dest_pf);
 
        pe->src_quals = build_edge_vertex_link_quals(eletup, pf->factorpos + 1, pf->src_pf->factorpos + 1,
                                                     pe->srcvertexid,
                                                     Anum_pg_propgraph_element_pgesrckey,
                                                     Anum_pg_propgraph_element_pgesrcref,
                                                     Anum_pg_propgraph_element_pgesrceqop);
        pe->dest_quals = build_edge_vertex_link_quals(eletup, pf->factorpos + 1, pf->dest_pf->factorpos + 1,
                                                      pe->destvertexid,
                                                      Anum_pg_propgraph_element_pgedestkey,
                                                      Anum_pg_propgraph_element_pgedestref,
                                                      Anum_pg_propgraph_element_pgedesteqop);
    }
 
    ReleaseSysCache(eletup);
 
    return pe;
}
 
/*
 * Returns the list of OIDs of graph labels which the given label expression
 * resolves to in the given property graph.
 */
static List *
get_labels_for_expr(Oid propgraphid, Node *labelexpr)
{
    List       *label_oids;
 
    if (!labelexpr)
    {
        Relation    rel;
        SysScanDesc scan;
        ScanKeyData key[1];
        HeapTuple   tup;
 
        /*
         * According to section 9.2 "Contextual inference of a set of labels"
         * subclause 2.a.ii of SQL/PGQ standard, element pattern which does
         * not have a label expression is considered to have label expression
         * equivalent to '%|!%' which is set of all labels.
         */
        label_oids = NIL;
        rel = table_open(PropgraphLabelRelationId, AccessShareLock);
        ScanKeyInit(&key[0],
                    Anum_pg_propgraph_label_pglpgid,
                    BTEqualStrategyNumber,
                    F_OIDEQ, ObjectIdGetDatum(propgraphid));
        scan = systable_beginscan(rel, PropgraphLabelGraphNameIndexId,
                                  true, NULL, 1, key);
        while (HeapTupleIsValid(tup = systable_getnext(scan)))
        {
            Form_pg_propgraph_label label = (Form_pg_propgraph_label) GETSTRUCT(tup);
 
            label_oids = lappend_oid(label_oids, label->oid);
        }
        systable_endscan(scan);
        table_close(rel, AccessShareLock);
    }
    else if (IsA(labelexpr, GraphLabelRef))
    {
        GraphLabelRef *glr = castNode(GraphLabelRef, labelexpr);
 
        label_oids = list_make1_oid(glr->labelid);
    }
    else if (IsA(labelexpr, BoolExpr))
    {
        BoolExpr   *be = castNode(BoolExpr, labelexpr);
        List       *label_exprs = be->args;
 
        label_oids = NIL;
        foreach_node(GraphLabelRef, glr, label_exprs)
            label_oids = lappend_oid(label_oids, glr->labelid);
    }
    else
    {
        /*
         * should not reach here since gram.y will not generate a label
         * expression with other node types.
         */
        elog(ERROR, "unsupported label expression node: %d", (int) nodeTag(labelexpr));
    }
 
    return label_oids;
}
 
/*
 * Return a list of all the graph elements that satisfy the graph element pattern
 * represented by the given path_factor `pf`.
 *
 * First we find all the graph labels that satisfy the label expression in path
 * factor. Each label is associated with one or more graph elements.  A union of
 * all such elements satisfies the element pattern. We create one path_element
 * object representing every element whose graph element kind qualifies the
 * element pattern kind. A list of all such path_element objects is returned.
 *
 * Note that we need to report an error for an explicitly specified label which
 * is not associated with any graph element of the required kind. So we have to
 * treat each label separately. Without that requirement we could have collected
 * all the unique elements first and then created path_element objects for them
 * to simplify the code.
 */
static List *
get_path_elements_for_path_factor(Oid propgraphid, struct path_factor *pf)
{
    List       *label_oids = get_labels_for_expr(propgraphid, pf->labelexpr);
    List       *elem_oids_seen = NIL;
    List       *pf_elem_oids = NIL;
    List       *path_elements = NIL;
    List       *unresolved_labels = NIL;
    Relation    rel;
    SysScanDesc scan;
    ScanKeyData key[1];
    HeapTuple   tup;
 
    /*
     * A property graph element can be either a vertex or an edge. Other types
     * of path factors like nested path pattern need to be handled separately
     * when supported.
     */
    Assert(pf->kind == VERTEX_PATTERN || IS_EDGE_PATTERN(pf->kind));
 
    rel = table_open(PropgraphElementLabelRelationId, AccessShareLock);
    foreach_oid(labeloid, label_oids)
    {
        bool        found = false;
 
        ScanKeyInit(&key[0],
                    Anum_pg_propgraph_element_label_pgellabelid,
                    BTEqualStrategyNumber,
                    F_OIDEQ, ObjectIdGetDatum(labeloid));
        scan = systable_beginscan(rel, PropgraphElementLabelLabelIndexId, true,
                                  NULL, 1, key);
        while (HeapTupleIsValid(tup = systable_getnext(scan)))
        {
            Form_pg_propgraph_element_label label_elem = (Form_pg_propgraph_element_label) GETSTRUCT(tup);
            Oid         elem_oid = label_elem->pgelelid;
 
            if (!list_member_oid(elem_oids_seen, elem_oid))
            {
                /*
                 * Create path_element object if the new element qualifies the
                 * element pattern kind.
                 */
                struct path_element *pe = create_pe_for_element(pf, elem_oid);
 
                if (pe)
                {
                    path_elements = lappend(path_elements, pe);
 
                    /* Remember qualified elements. */
                    pf_elem_oids = lappend_oid(pf_elem_oids, elem_oid);
                    found = true;
                }
 
                /*
                 * Remember qualified and unqualified elements processed so
                 * far to avoid processing already processed elements again.
                 */
                elem_oids_seen = lappend_oid(elem_oids_seen, label_elem->pgelelid);
            }
            else if (list_member_oid(pf_elem_oids, elem_oid))
            {
                /*
                 * The graph element is known to qualify the given element
                 * pattern. Flag that the current label has at least one
                 * qualified element associated with it.
                 */
                found = true;
            }
        }
 
        if (!found)
        {
            /*
             * We did not find any qualified element associated with this
             * label. The label or its properties can not be associated with
             * the given element pattern. Throw an error if the label was
             * explicitly specified in the element pattern. Otherwise remember
             * it for later use.
             */
            if (!pf->labelexpr)
                unresolved_labels = lappend_oid(unresolved_labels, labeloid);
            else
                ereport(ERROR,
                        (errcode(ERRCODE_UNDEFINED_OBJECT),
                         errmsg("no property graph element of type \"%s\" has label \"%s\" associated with it in property graph \"%s\"",
                                pf->kind == VERTEX_PATTERN ? "vertex" : "edge",
                                get_propgraph_label_name(labeloid),
                                get_rel_name(propgraphid))));
        }
 
        systable_endscan(scan);
    }
    table_close(rel, AccessShareLock);
 
    /*
     * Remove the labels which were not explicitly mentioned in the label
     * expression but do not have any qualified elements associated with them.
     * Properties associated with such labels may not be referenced. See
     * replace_property_refs_mutator() for more details.
     */
    pf->labeloids = list_difference_oid(label_oids, unresolved_labels);
 
    return path_elements;
}
 
/*
 * Mutating property references into table variables
 */
 
struct replace_property_refs_context
{
    Oid         propgraphid;
    const List *mappings;
};
 
static Node *
replace_property_refs_mutator(Node *node, struct replace_property_refs_context *context)
{
    if (node == NULL)
        return NULL;
    if (IsA(node, Var))
    {
        Var        *var = (Var *) node;
        Var        *newvar = copyObject(var);
 
        /*
         * If it's already a Var, then it was a lateral reference.  Since we
         * are in a subquery after the rewrite, we have to increase the level
         * by one.
         */
        newvar->varlevelsup++;
 
        return (Node *) newvar;
    }
    else if (IsA(node, GraphPropertyRef))
    {
        GraphPropertyRef *gpr = (GraphPropertyRef *) node;
        Node       *n = NULL;
        struct path_element *found_mapping = NULL;
        struct path_factor *mapping_factor = NULL;
        List       *unrelated_labels = NIL;
 
        foreach_ptr(struct path_element, m, context->mappings)
        {
            if (m->path_factor->variable && strcmp(gpr->elvarname, m->path_factor->variable) == 0)
            {
                found_mapping = m;
                break;
            }
        }
 
        /*
         * transformGraphTablePropertyRef() would not create a
         * GraphPropertyRef for a variable which is not present in the graph
         * path pattern.
         */
        Assert(found_mapping);
 
        mapping_factor = found_mapping->path_factor;
 
        /*
         * Find property definition for given element through any of the
         * associated labels qualifying the given element pattern.
         */
        foreach_oid(labeloid, mapping_factor->labeloids)
        {
            Oid         elem_labelid = GetSysCacheOid2(PROPGRAPHELEMENTLABELELEMENTLABEL,
                                                       Anum_pg_propgraph_element_label_oid,
                                                       ObjectIdGetDatum(found_mapping->elemoid),
                                                       ObjectIdGetDatum(labeloid));
 
            if (OidIsValid(elem_labelid))
            {
                HeapTuple   tup = SearchSysCache2(PROPGRAPHLABELPROP, ObjectIdGetDatum(elem_labelid),
                                                  ObjectIdGetDatum(gpr->propid));
 
                if (!tup)
                {
                    /*
                     * The label is associated with the given element but it
                     * is not associated with the required property. Check
                     * next label.
                     */
                    continue;
                }
 
                n = stringToNode(TextDatumGetCString(SysCacheGetAttrNotNull(PROPGRAPHLABELPROP,
                                                                            tup, Anum_pg_propgraph_label_property_plpexpr)));
                ChangeVarNodes(n, 1, mapping_factor->factorpos + 1, 0);
 
                ReleaseSysCache(tup);
            }
            else
            {
                /*
                 * Label is not associated with the element but it may be
                 * associated with the property through some other element.
                 * Save it for later use.
                 */
                unrelated_labels = lappend_oid(unrelated_labels, labeloid);
            }
        }
 
        /* See if we can resolve the property in some other way. */
        if (!n)
        {
            bool        prop_associated = false;
 
            foreach_oid(loid, unrelated_labels)
            {
                if (is_property_associated_with_label(loid, gpr->propid))
                {
                    prop_associated = true;
                    break;
                }
            }
 
            if (prop_associated)
            {
                /*
                 * The property is associated with at least one of the labels
                 * that satisfy given element pattern. If it's associated with
                 * the given element (through some other label), use
                 * corresponding value expression. Otherwise NULL. Ref.
                 * SQL/PGQ standard section 6.5 Property Reference, General
                 * Rule 2.b.
                 */
                n = get_element_property_expr(found_mapping->elemoid, gpr->propid,
                                              mapping_factor->factorpos + 1);
 
                if (!n)
                    n = (Node *) makeNullConst(gpr->typeId, gpr->typmod, gpr->collation);
            }
 
        }
 
        if (!n)
            ereport(ERROR,
                    errcode(ERRCODE_UNDEFINED_OBJECT),
                    errmsg("property \"%s\" for element variable \"%s\" not found",
                           get_propgraph_property_name(gpr->propid), mapping_factor->variable));
 
        return n;
    }
 
    return expression_tree_mutator(node, replace_property_refs_mutator, context);
}
 
static Node *
replace_property_refs(Oid propgraphid, Node *node, const List *mappings)
{
    struct replace_property_refs_context context;
 
    context.mappings = mappings;
    context.propgraphid = propgraphid;
 
    return expression_tree_mutator(node, replace_property_refs_mutator, &context);
}
 
/*
 * Build join qualification expressions between edge and vertex tables.
 */
static List *
build_edge_vertex_link_quals(HeapTuple edgetup, int edgerti, int refrti, Oid refid, AttrNumber catalog_key_attnum, AttrNumber catalog_ref_attnum, AttrNumber catalog_eqop_attnum)
{
    List       *quals = NIL;
    Form_pg_propgraph_element pgeform;
    Datum       datum;
    Datum      *d1,
               *d2,
               *d3;
    int         n1,
                n2,
                n3;
    ParseState *pstate = make_parsestate(NULL);
    Oid         refrelid = GetSysCacheOid1(PROPGRAPHELOID, Anum_pg_propgraph_element_pgerelid, ObjectIdGetDatum(refid));
 
    pgeform = (Form_pg_propgraph_element) GETSTRUCT(edgetup);
 
    datum = SysCacheGetAttrNotNull(PROPGRAPHELOID, edgetup, catalog_key_attnum);
    deconstruct_array_builtin(DatumGetArrayTypeP(datum), INT2OID, &d1, NULL, &n1);
 
    datum = SysCacheGetAttrNotNull(PROPGRAPHELOID, edgetup, catalog_ref_attnum);
    deconstruct_array_builtin(DatumGetArrayTypeP(datum), INT2OID, &d2, NULL, &n2);
 
    datum = SysCacheGetAttrNotNull(PROPGRAPHELOID, edgetup, catalog_eqop_attnum);
    deconstruct_array_builtin(DatumGetArrayTypeP(datum), OIDOID, &d3, NULL, &n3);
 
    if (n1 != n2)
        elog(ERROR, "array size key (%d) vs ref (%d) mismatch for element ID %u", catalog_key_attnum, catalog_ref_attnum, pgeform->oid);
    if (n1 != n3)
        elog(ERROR, "array size key (%d) vs operator (%d) mismatch for element ID %u", catalog_key_attnum, catalog_eqop_attnum, pgeform->oid);
 
    for (int i = 0; i < n1; i++)
    {
        AttrNumber  keyattn = DatumGetInt16(d1[i]);
        AttrNumber  refattn = DatumGetInt16(d2[i]);
        Oid         eqop = DatumGetObjectId(d3[i]);
        Var        *keyvar;
        Var        *refvar;
        Oid         atttypid;
        int32       atttypmod;
        Oid         attcoll;
        HeapTuple   tup;
        Form_pg_operator opform;
        List       *args;
        Oid         actual_arg_types[2];
        Oid         declared_arg_types[2];
        OpExpr     *linkqual;
 
        get_atttypetypmodcoll(pgeform->pgerelid, keyattn, &atttypid, &atttypmod, &attcoll);
        keyvar = makeVar(edgerti, keyattn, atttypid, atttypmod, attcoll, 0);
        get_atttypetypmodcoll(refrelid, refattn, &atttypid, &atttypmod, &attcoll);
        refvar = makeVar(refrti, refattn, atttypid, atttypmod, attcoll, 0);
 
        tup = SearchSysCache1(OPEROID, ObjectIdGetDatum(eqop));
        if (!HeapTupleIsValid(tup))
            elog(ERROR, "cache lookup failed for operator %u", eqop);
        opform = (Form_pg_operator) GETSTRUCT(tup);
        /* An equality operator is a binary operator returning boolean result. */
        Assert(opform->oprkind == 'b'
               && RegProcedureIsValid(opform->oprcode)
               && opform->oprresult == BOOLOID
               && !get_func_retset(opform->oprcode));
 
        /*
         * Prepare operands and cast them to the types required by the
         * equality operator. Similar to PK/FK quals, referenced vertex key is
         * used as left operand and referencing edge key is used as right
         * operand.
         */
        args = list_make2(refvar, keyvar);
        actual_arg_types[0] = exprType((Node *) refvar);
        actual_arg_types[1] = exprType((Node *) keyvar);
        declared_arg_types[0] = opform->oprleft;
        declared_arg_types[1] = opform->oprright;
        make_fn_arguments(pstate, args, actual_arg_types, declared_arg_types);
 
        linkqual = makeNode(OpExpr);
        linkqual->opno = opform->oid;
        linkqual->opfuncid = opform->oprcode;
        linkqual->opresulttype = opform->oprresult;
        linkqual->opretset = false;
        /* opcollid and inputcollid will be set by parse_collate.c */
        linkqual->args = args;
        linkqual->location = -1;
 
        ReleaseSysCache(tup);
        quals = lappend(quals, linkqual);
    }
 
    assign_expr_collations(pstate, (Node *) quals);
 
    return quals;
}
 
/*
 * Check if the given property is associated with the given label.
 *
 * A label projects the same set of properties through every element it is
 * associated with. Find any of the elements and return true if that element is
 * associated with the given property. False otherwise.
 */
static bool
is_property_associated_with_label(Oid labeloid, Oid propoid)
{
    Relation    rel;
    SysScanDesc scan;
    ScanKeyData key[1];
    HeapTuple   tup;
    bool        associated = false;
 
    rel = table_open(PropgraphElementLabelRelationId, RowShareLock);
    ScanKeyInit(&key[0],
                Anum_pg_propgraph_element_label_pgellabelid,
                BTEqualStrategyNumber,
                F_OIDEQ, ObjectIdGetDatum(labeloid));
    scan = systable_beginscan(rel, PropgraphElementLabelLabelIndexId,
                              true, NULL, 1, key);
 
    if (HeapTupleIsValid(tup = systable_getnext(scan)))
    {
        Form_pg_propgraph_element_label ele_label = (Form_pg_propgraph_element_label) GETSTRUCT(tup);
 
        associated = SearchSysCacheExists2(PROPGRAPHLABELPROP,
                                           ObjectIdGetDatum(ele_label->oid), ObjectIdGetDatum(propoid));
    }
    systable_endscan(scan);
    table_close(rel, RowShareLock);
 
    return associated;
}
 
/*
 * If given element has the given property associated with it, through any of
 * the associated labels, return value expression of the property. Otherwise
 * NULL.
 */
static Node *
get_element_property_expr(Oid elemoid, Oid propoid, int rtindex)
{
    Relation    rel;
    SysScanDesc scan;
    ScanKeyData key[1];
    HeapTuple   labeltup;
    Node       *n = NULL;
 
    rel = table_open(PropgraphElementLabelRelationId, RowShareLock);
    ScanKeyInit(&key[0],
                Anum_pg_propgraph_element_label_pgelelid,
                BTEqualStrategyNumber,
                F_OIDEQ, ObjectIdGetDatum(elemoid));
    scan = systable_beginscan(rel, PropgraphElementLabelElementLabelIndexId,
                              true, NULL, 1, key);
 
    while (HeapTupleIsValid(labeltup = systable_getnext(scan)))
    {
        Form_pg_propgraph_element_label ele_label = (Form_pg_propgraph_element_label) GETSTRUCT(labeltup);
 
        HeapTuple   proptup = SearchSysCache2(PROPGRAPHLABELPROP,
                                              ObjectIdGetDatum(ele_label->oid), ObjectIdGetDatum(propoid));
 
        if (!proptup)
            continue;
        n = stringToNode(TextDatumGetCString(SysCacheGetAttrNotNull(PROPGRAPHLABELPROP,
                                                                    proptup, Anum_pg_propgraph_label_property_plpexpr)));
        ChangeVarNodes(n, 1, rtindex, 0);
 
        ReleaseSysCache(proptup);
        break;
    }
    systable_endscan(scan);
    table_close(rel, RowShareLock);
 
    return n;
}