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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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28
src/backend/optimizer/util/clauses.c
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@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.164 2004/03/14 23:41:27 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.165 2004/03/17 20:48:42 tgl Exp $
*
* HISTORY
* AUTHOR DATE MAJOR EVENT
@@ -1397,15 +1397,29 @@ eval_const_expressions_mutator(Node *node, List *active_fns)
* simplify the entire CASE to that alternative's expression.
* If there are no non-FALSE alternatives, we simplify the entire
* CASE to the default result (ELSE result).
*
* If we have a simple-form CASE with constant test expression and
* one or more constant comparison expressions, we could run the
* implied comparisons and potentially reduce those arms to constants.
* This is not yet implemented, however. At present, the
* CaseTestExpr placeholder will always act as a non-constant node
* and prevent the comparison boolean expressions from being reduced
* to Const nodes.
*----------
*/
CaseExpr *caseexpr = (CaseExpr *) node;
CaseExpr *newcase;
Node *newarg;
FastList newargs;
Node *defresult;
Const *const_input;
List *arg;
/* Simplify the test expression, if any */
newarg = eval_const_expressions_mutator((Node *) caseexpr->arg,
active_fns);
/* Simplify the WHEN clauses */
FastListInit(&newargs);
foreach(arg, caseexpr->args)
{
@@ -1454,7 +1468,7 @@ eval_const_expressions_mutator(Node *node, List *active_fns)
/* Otherwise we need a new CASE node */
newcase = makeNode(CaseExpr);
newcase->casetype = caseexpr->casetype;
newcase->arg = NULL;
newcase->arg = (Expr *) newarg;
newcase->args = FastListValue(&newargs);
newcase->defresult = (Expr *) defresult;
return (Node *) newcase;
@@ -2319,6 +2333,7 @@ expression_tree_walker(Node *node,
case T_Const:
case T_Param:
case T_CoerceToDomainValue:
case T_CaseTestExpr:
case T_SetToDefault:
case T_RangeTblRef:
/* primitive node types with no subnodes */
@@ -2425,6 +2440,8 @@ expression_tree_walker(Node *node,
{
CaseExpr *caseexpr = (CaseExpr *) node;
if (walker(caseexpr->arg, context))
return true;
/* we assume walker doesn't care about CaseWhens, either */
foreach(temp, caseexpr->args)
{
@@ -2436,9 +2453,6 @@ expression_tree_walker(Node *node,
if (walker(when->result, context))
return true;
}
/* caseexpr->arg should be null, but we'll check it anyway */
if (walker(caseexpr->arg, context))
return true;
if (walker(caseexpr->defresult, context))
return true;
}
@@ -2692,6 +2706,7 @@ expression_tree_mutator(Node *node,
case T_Const:
case T_Param:
case T_CoerceToDomainValue:
case T_CaseTestExpr:
case T_SetToDefault:
case T_RangeTblRef:
/* primitive node types with no subnodes */
@@ -2829,9 +2844,8 @@ expression_tree_mutator(Node *node,
CaseExpr *newnode;
FLATCOPY(newnode, caseexpr, CaseExpr);
MUTATE(newnode->args, caseexpr->args, List *);
/* caseexpr->arg should be null, but we'll check it anyway */
MUTATE(newnode->arg, caseexpr->arg, Expr *);
MUTATE(newnode->args, caseexpr->args, List *);
MUTATE(newnode->defresult, caseexpr->defresult, Expr *);
return (Node *) newnode;
}