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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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62
src/backend/parser/parse_expr.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/parser/parse_expr.c,v 1.165 2004/02/13 01:08:20 tgl Exp $
* $PostgreSQL: pgsql/src/backend/parser/parse_expr.c,v 1.166 2004/03/17 20:48:42 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -637,14 +637,39 @@ transformExpr(ParseState *pstate, Node *expr)
case T_CaseExpr:
{
CaseExpr *c = (CaseExpr *) expr;
CaseExpr *newc = makeNode(CaseExpr);
List *newargs = NIL;
List *typeids = NIL;
CaseExpr *newc;
Node *arg;
CaseTestExpr *placeholder;
List *newargs;
List *typeids;
List *args;
Node *defresult;
Oid ptype;
/* If we already transformed this node, do nothing */
if (OidIsValid(c->casetype))
{
result = expr;
break;
}
newc = makeNode(CaseExpr);
/* transform the test expression, if any */
arg = transformExpr(pstate, (Node *) c->arg);
newc->arg = (Expr *) arg;
/* generate placeholder for test expression */
if (arg)
{
placeholder = makeNode(CaseTestExpr);
placeholder->typeId = exprType(arg);
placeholder->typeMod = exprTypmod(arg);
}
else
placeholder = NULL;
/* transform the list of arguments */
newargs = NIL;
typeids = NIL;
foreach(args, c->args)
{
CaseWhen *w = (CaseWhen *) lfirst(args);
@ -654,11 +679,11 @@ transformExpr(ParseState *pstate, Node *expr)
Assert(IsA(w, CaseWhen));
warg = (Node *) w->expr;
if (c->arg != NULL)
if (placeholder)
{
/* shorthand form was specified, so expand... */
warg = (Node *) makeSimpleA_Expr(AEXPR_OP, "=",
(Node *) c->arg,
(Node *) placeholder,
warg);
}
neww->expr = (Expr *) transformExpr(pstate, warg);
@ -667,18 +692,7 @@ transformExpr(ParseState *pstate, Node *expr)
(Node *) neww->expr,
"CASE/WHEN");
/*
* result is NULL for NULLIF() construct - thomas
* 1998-11-11
*/
warg = (Node *) w->result;
if (warg == NULL)
{
A_Const *n = makeNode(A_Const);
n->val.type = T_Null;
warg = (Node *) n;
}
neww->result = (Expr *) transformExpr(pstate, warg);
newargs = lappend(newargs, neww);
@ -687,13 +701,6 @@ transformExpr(ParseState *pstate, Node *expr)
newc->args = newargs;
/*
* It's not shorthand anymore, so drop the implicit
* argument. This is necessary to keep any re-application
* of transformExpr from doing the wrong thing.
*/
newc->arg = NULL;
/* transform the default clause */
defresult = (Node *) c->defresult;
if (defresult == NULL)
@ -714,6 +721,7 @@ transformExpr(ParseState *pstate, Node *expr)
typeids = lconso(exprType((Node *) newc->defresult), typeids);
ptype = select_common_type(typeids, "CASE");
Assert(OidIsValid(ptype));
newc->casetype = ptype;
/* Convert default result clause, if necessary */
@ -915,6 +923,7 @@ transformExpr(ParseState *pstate, Node *expr)
case T_BoolExpr:
case T_FieldSelect:
case T_RelabelType:
case T_CaseTestExpr:
case T_CoerceToDomain:
case T_CoerceToDomainValue:
case T_SetToDefault:
@ -1288,6 +1297,9 @@ exprType(Node *expr)
case T_CaseWhen:
type = exprType((Node *) ((CaseWhen *) expr)->result);
break;
case T_CaseTestExpr:
type = ((CaseTestExpr *) expr)->typeId;
break;
case T_ArrayExpr:
type = ((ArrayExpr *) expr)->array_typeid;
break;
@ -1408,6 +1420,8 @@ exprTypmod(Node *expr)
return typmod;
}
break;
case T_CaseTestExpr:
return ((CaseTestExpr *) expr)->typeMod;
case T_CoalesceExpr:
{
/*