mirror of https://github.com/postgres/postgres
If we're cleaning out _deadcode, might as well zap this one too.
This commit is contained in:
Tom Lane
parent
45e584a445
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/*-------------------------------------------------------------------------
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*
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* prepkeyset.c
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* Special preparation for keyset queries (KSQO).
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*
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* Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*-------------------------------------------------------------------------
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*/
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/* THIS FILE WAS USED FOR KSQO, WHICH IS DISABLED NOW. bjm 2002-06-15 */
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#include "postgres.h"
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#include "optimizer/planmain.h"
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bool _use_keyset_query_optimizer = FALSE;
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#ifdef ENABLE_KEY_SET_QUERY
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static int inspectOpNode(Expr *expr);
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static int inspectAndNode(Expr *expr);
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static int inspectOrNode(Expr *expr);
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static int TotalExpr;
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/**********************************************************************
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* This routine transforms query trees with the following form:
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* SELECT a,b, ... FROM one_table WHERE
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* (v1 = const1 AND v2 = const2 [ vn = constn ]) OR
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* (v1 = const3 AND v2 = const4 [ vn = constn ]) OR
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* (v1 = const5 AND v2 = const6 [ vn = constn ]) OR
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* ...
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* [(v1 = constn AND v2 = constn [ vn = constn ])]
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*
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* into
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*
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* SELECT a,b, ... FROM one_table WHERE
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* (v1 = const1 AND v2 = const2 [ vn = constn ]) UNION
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* SELECT a,b, ... FROM one_table WHERE
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* (v1 = const3 AND v2 = const4 [ vn = constn ]) UNION
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* SELECT a,b, ... FROM one_table WHERE
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* (v1 = const5 AND v2 = const6 [ vn = constn ]) UNION
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* ...
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* SELECT a,b, ... FROM one_table WHERE
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* [(v1 = constn AND v2 = constn [ vn = constn ])]
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*
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*
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* To qualify for transformation the query must not be a sub select,
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* a HAVING, or a GROUP BY. It must be a single table and have KSQO
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* set to 'on'.
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*
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* The primary use of this transformation is to avoid the exponential
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* memory consumption of cnfify() and to make use of index access
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* methods.
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*
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* daveh@insightdist.com 1998-08-31
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*
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* May want to also prune out duplicate terms.
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*
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* XXX: this code is currently not compiled because it has not been
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* updated to work with the re-implementation of UNION/INTERSECT/EXCEPT
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* in PostgreSQL 7.1. However, it is of questionable value in any
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* case, because it changes the semantics of the original query:
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* UNION will add an implicit SELECT DISTINCT, which might change
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* the results that are returned.
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**********************************************************************/
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void
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transformKeySetQuery(Query *origNode)
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{
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/* Qualify as a key set query candidate */
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if (_use_keyset_query_optimizer == FALSE ||
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origNode->groupClause ||
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origNode->havingQual ||
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origNode->hasAggs ||
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origNode->utilityStmt ||
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origNode->unionClause ||
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origNode->unionall ||
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origNode->hasSubLinks ||
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origNode->commandType != CMD_SELECT)
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return;
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/* Qualify single table query */
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if (length(origNode->rtable) != 1)
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return;
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/* Sorry about the global, not worth passing around */
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/* 9 expressions seems like a good number. More than 9 */
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/* and it starts to slow down quite a bit */
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TotalExpr = 0;
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/*************************/
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/* Qualify where clause */
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/*************************/
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if (!inspectOrNode((Expr *) origNode->jointree->quals) || TotalExpr < 9)
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return;
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/* Copy essential elements into a union node */
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while (((Expr *) origNode->jointree->quals)->opType == OR_EXPR)
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{
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Query *unionNode = makeNode(Query);
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List *qualargs = ((Expr *) origNode->jointree->quals)->args;
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unionNode->commandType = origNode->commandType;
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unionNode->resultRelation = origNode->resultRelation;
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unionNode->isPortal = origNode->isPortal;
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unionNode->isBinary = origNode->isBinary;
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Node_Copy(origNode, unionNode, distinctClause);
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Node_Copy(origNode, unionNode, sortClause);
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Node_Copy(origNode, unionNode, rtable);
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origNode->jointree->quals = NULL; /* avoid unnecessary
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* copying */
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Node_Copy(origNode, unionNode, jointree);
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Node_Copy(origNode, unionNode, targetList);
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/* Pull up Expr = */
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unionNode->jointree->quals = lsecond(qualargs);
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/* Pull up balance of tree */
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origNode->jointree->quals = lfirst(qualargs);
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origNode->unionClause = lappend(origNode->unionClause, unionNode);
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}
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return;
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}
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static int
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/**********************************************************************
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* Checks for 1 or more OR terms w/ 1 or more AND terms.
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* AND terms must be equal in size.
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* Returns the number of each AND term.
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**********************************************************************/
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inspectOrNode(Expr *expr)
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{
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int rc;
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Expr *firstExpr,
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*secondExpr;
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if (!(expr && nodeTag(expr) == T_Expr && expr->opType == OR_EXPR))
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return 0;
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firstExpr = lfirst(expr->args);
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secondExpr = lsecond(expr->args);
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if (nodeTag(firstExpr) != T_Expr || nodeTag(secondExpr) != T_Expr)
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return 0;
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if (firstExpr->opType == OR_EXPR && secondExpr->opType == AND_EXPR)
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{
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if ((rc = inspectOrNode(firstExpr)) == 0)
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return 0;
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return (rc == inspectAndNode(secondExpr)) ? rc : 0;
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}
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else if (firstExpr->opType == AND_EXPR && secondExpr->opType == AND_EXPR)
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{
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if ((rc = inspectAndNode(firstExpr)) == 0)
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return 0;
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return (rc == inspectAndNode(secondExpr)) ? rc : 0;
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}
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return 0;
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}
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static int
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/**********************************************************************
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* Check for one or more AND terms. Each sub-term must be a T_Const
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* T_Var expression.
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* Returns the number of AND terms.
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**********************************************************************/
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inspectAndNode(Expr *expr)
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{
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int rc;
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Expr *firstExpr,
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*secondExpr;
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if (!(expr && nodeTag(expr) == T_Expr && expr->opType == AND_EXPR))
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return 0;
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firstExpr = lfirst(expr->args);
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secondExpr = lsecond(expr->args);
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if (nodeTag(firstExpr) != T_Expr || nodeTag(secondExpr) != T_Expr)
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return 0;
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if (firstExpr->opType == AND_EXPR &&
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secondExpr->opType == OP_EXPR && inspectOpNode(secondExpr))
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{
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rc = inspectAndNode(firstExpr);
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return ((rc) ? (rc + 1) : 0); /* Add up the AND nodes */
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}
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else if (firstExpr->opType == OP_EXPR && inspectOpNode(firstExpr) &&
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secondExpr->opType == OP_EXPR && inspectOpNode(secondExpr))
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return 1;
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return 0;
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}
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static int
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/******************************************************************
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* Return TRUE if T_Var = T_Const, else FALSE
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* Actually it does not test for =. Need to do this!
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******************************************************************/
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inspectOpNode(Expr *expr)
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{
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Expr *firstExpr,
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*secondExpr;
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if (nodeTag(expr) != T_Expr || expr->opType != OP_EXPR)
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return FALSE;
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TotalExpr++;
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firstExpr = lfirst(expr->args);
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secondExpr = lsecond(expr->args);
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return (firstExpr && secondExpr && nodeTag(firstExpr) == T_Var && nodeTag(secondExpr) == T_Const);
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}
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#endif /* ENABLE_KEY_SET_QUERY */
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