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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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37
src/include/nodes/primnodes.h
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@@ -10,7 +10,7 @@
* Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/nodes/primnodes.h,v 1.95 2004/03/14 23:41:27 tgl Exp $
* $PostgreSQL: pgsql/src/include/nodes/primnodes.h,v 1.96 2004/03/17 20:48:43 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -563,8 +563,27 @@ typedef struct RelabelType
CoercionForm relabelformat; /* how to display this node */
} RelabelType;
/*
/*----------
* CaseExpr - a CASE expression
*
* We support two distinct forms of CASE expression:
* CASE WHEN boolexpr THEN expr [ WHEN boolexpr THEN expr ... ]
* CASE testexpr WHEN compexpr THEN expr [ WHEN compexpr THEN expr ... ]
* These are distinguishable by the "arg" field being NULL in the first case
* and the testexpr in the second case.
*
* In the raw grammar output for the second form, the condition expressions
* of the WHEN clauses are just the comparison values. Parse analysis
* converts these to valid boolean expressions of the form
* CaseTestExpr '=' compexpr
* where the CaseTestExpr node is a placeholder that emits the correct
* value at runtime. This structure is used so that the testexpr need be
* evaluated only once. Note that after parse analysis, the condition
* expressions always yield boolean.
*
* Note: we can test whether a CaseExpr has been through parse analysis
* yet by checking whether casetype is InvalidOid or not.
*----------
*/
typedef struct CaseExpr
{
@@ -576,7 +595,7 @@ typedef struct CaseExpr
} CaseExpr;
/*
* CaseWhen - an argument to a CASE expression
* CaseWhen - one arm of a CASE expression
*/
typedef struct CaseWhen
{
@@ -585,6 +604,18 @@ typedef struct CaseWhen
Expr *result; /* substitution result */
} CaseWhen;
/*
* Placeholder node for the test value to be processed by a CASE expression.
* This is effectively like a Param, but can be implemented more simply
* since we need only one replacement value at a time.
*/
typedef struct CaseTestExpr
{
Expr xpr;
Oid typeId; /* type for substituted value */
int32 typeMod; /* typemod for substituted value */
} CaseTestExpr;
/*
* ArrayExpr - an ARRAY[] expression
*