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Reimplement CASE val WHEN compval1 THEN ... WHEN compval2 THEN ... END

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so that the 'val' is computed only once, per recent discussion.  The
speedup is not much when 'val' is just a simple variable, but could be
significant for larger expressions.  More importantly this avoids issues
with multiple evaluations of a volatile 'val', and it allows the CASE
expression to be reverse-listed in its original form by ruleutils.c.
This commit is contained in:
Tom Lane
2004-03-17 20:48:43 +00:00
parent 8c702ea7ac
commit 55f7c3300d
16 changed files with 248 additions and 55 deletions
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52
src/backend/executor/execQual.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.155 2004/03/17 01:02:23 tgl Exp $
* $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.156 2004/03/17 20:48:42 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -81,6 +81,9 @@ static Datum ExecEvalAnd(BoolExprState *andExpr, ExprContext *econtext,
bool *isNull, ExprDoneCond *isDone);
static Datum ExecEvalCase(CaseExprState *caseExpr, ExprContext *econtext,
bool *isNull, ExprDoneCond *isDone);
static Datum ExecEvalCaseTestExpr(ExprState *exprstate,
ExprContext *econtext,
bool *isNull, ExprDoneCond *isDone);
static Datum ExecEvalArray(ArrayExprState *astate,
ExprContext *econtext,
bool *isNull, ExprDoneCond *isDone);
@ -1809,10 +1812,29 @@ ExecEvalCase(CaseExprState *caseExpr, ExprContext *econtext,
{
List *clauses = caseExpr->args;
List *clause;
Datum save_datum;
bool save_isNull;
if (isDone)
*isDone = ExprSingleResult;
/*
* If there's a test expression, we have to evaluate it and save
* the value where the CaseTestExpr placeholders can find it.
* We must save and restore prior setting of econtext's caseValue fields,
* in case this node is itself within a larger CASE.
*/
save_datum = econtext->caseValue_datum;
save_isNull = econtext->caseValue_isNull;
if (caseExpr->arg)
{
econtext->caseValue_datum = ExecEvalExpr(caseExpr->arg,
econtext,
&econtext->caseValue_isNull,
NULL);
}
/*
* we evaluate each of the WHEN clauses in turn, as soon as one is
* true we return the corresponding result. If none are true then we
@ -1835,6 +1857,8 @@ ExecEvalCase(CaseExprState *caseExpr, ExprContext *econtext,
*/
if (DatumGetBool(clause_value) && !*isNull)
{
econtext->caseValue_datum = save_datum;
econtext->caseValue_isNull = save_isNull;
return ExecEvalExpr(wclause->result,
econtext,
isNull,
@ -1842,6 +1866,9 @@ ExecEvalCase(CaseExprState *caseExpr, ExprContext *econtext,
}
}
econtext->caseValue_datum = save_datum;
econtext->caseValue_isNull = save_isNull;
if (caseExpr->defresult)
{
return ExecEvalExpr(caseExpr->defresult,
@ -1854,6 +1881,22 @@ ExecEvalCase(CaseExprState *caseExpr, ExprContext *econtext,
return (Datum) 0;
}
/*
* ExecEvalCaseTestExpr
*
* Return the value stored by CASE.
*/
static Datum
ExecEvalCaseTestExpr(ExprState *exprstate,
ExprContext *econtext,
bool *isNull, ExprDoneCond *isDone)
{
if (isDone)
*isDone = ExprSingleResult;
*isNull = econtext->caseValue_isNull;
return econtext->caseValue_datum;
}
/* ----------------------------------------------------------------
* ExecEvalArray - ARRAY[] expressions
*
@ -2478,6 +2521,10 @@ ExecInitExpr(Expr *node, PlanState *parent)
state = (ExprState *) makeNode(ExprState);
state->evalfunc = ExecEvalCoerceToDomainValue;
break;
case T_CaseTestExpr:
state = (ExprState *) makeNode(ExprState);
state->evalfunc = ExecEvalCaseTestExpr;
break;
case T_Aggref:
{
Aggref *aggref = (Aggref *) node;
@ -2666,6 +2713,7 @@ ExecInitExpr(Expr *node, PlanState *parent)
List *inlist;
cstate->xprstate.evalfunc = (ExprStateEvalFunc) ExecEvalCase;
cstate->arg = ExecInitExpr(caseexpr->arg, parent);
FastListInit(&outlist);
foreach(inlist, caseexpr->args)
{
@ -2680,8 +2728,6 @@ ExecInitExpr(Expr *node, PlanState *parent)
FastAppend(&outlist, wstate);
}
cstate->args = FastListValue(&outlist);
/* caseexpr->arg should be null by now */
Assert(caseexpr->arg == NULL);
cstate->defresult = ExecInitExpr(caseexpr->defresult, parent);
state = (ExprState *) cstate;
}