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Implement CASE expression.

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This commit is contained in:
Thomas G. Lockhart
1998-12-04 15:34:49 +00:00
parent 19740e2fff
commit bedd04a551
17 changed files with 779 additions and 110 deletions
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87
src/backend/executor/execQual.c
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@ -7,7 +7,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/executor/execQual.c,v 1.38 1998/11/27 19:52:00 vadim Exp $
* $Header: /cvsroot/pgsql/src/backend/executor/execQual.c,v 1.39 1998/12/04 15:33:19 thomas Exp $
*
*-------------------------------------------------------------------------
*/
@ -20,7 +20,7 @@
* NOTES
* ExecEvalExpr() and ExecEvalVar() are hotspots. making these faster
* will speed up the entire system. Unfortunately they are currently
* implemented recursively.. Eliminating the recursion is bound to
* implemented recursively. Eliminating the recursion is bound to
* improve the speed of the executor.
*
* ExecTargetList() is used to make tuple projections. Rather then
@ -205,7 +205,7 @@ ExecEvalAggreg(Aggreg *agg, ExprContext *econtext, bool *isNull)
* variable with respect to given expression context.
*
*
* As an entry condition, we expect that the the datatype the
* As an entry condition, we expect that the datatype the
* plan expects to get (as told by our "variable" argument) is in
* fact the datatype of the attribute the plan says to fetch (as
* seen in the current context, identified by our "econtext"
@ -1124,6 +1124,79 @@ ExecEvalAnd(Expr *andExpr, ExprContext *econtext, bool *isNull)
return const_value;
}
/* ----------------------------------------------------------------
* ExecEvalCase
*
* Evaluate a CASE clause. Will have boolean expressions
* inside the WHEN clauses, and will have constants
* for results.
* - thomas 1998-11-09
* ----------------------------------------------------------------
*/
static Datum
ExecEvalCase(CaseExpr *caseExpr, ExprContext *econtext, bool *isNull)
{
List *clauses;
List *clause;
CaseWhen *wclause;
Datum const_value = 0;
bool isDone;
clauses = caseExpr->args;
/******************
* 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 return the value
* of the default clause, or NULL.
******************
*/
foreach(clause, clauses)
{
/******************
* We don't iterate over sets in the quals, so pass in an isDone
* flag, but ignore it.
******************
*/
wclause = lfirst(clause);
const_value = ExecEvalExpr((Node *) wclause->expr,
econtext,
isNull,
&isDone);
/******************
* if we have a true test, then we return the result,
* since the case statement is satisfied.
******************
*/
if (DatumGetInt32(const_value) != 0)
{
const_value = ExecEvalExpr((Node *) wclause->result,
econtext,
isNull,
&isDone);
return (Datum) const_value;
}
}
if (caseExpr->defresult)
{
const_value = ExecEvalExpr((Node *) caseExpr->defresult,
econtext,
isNull,
&isDone);
}
else
{
*isNull = true;
}
return const_value;
}
/* ----------------------------------------------------------------
* ExecEvalExpr
*
@ -1236,13 +1309,18 @@ ExecEvalExpr(Node *expression,
}
break;
}
case T_CaseExpr:
retDatum = (Datum) ExecEvalCase((CaseExpr *) expression, econtext, isNull);
break;
default:
elog(ERROR, "ExecEvalExpr: unknown expression type %d", nodeTag(expression));
break;
}
return retDatum;
}
} /* ExecEvalExpr() */
/* ----------------------------------------------------------------
* ExecQual / ExecTargetList
@ -1642,3 +1720,4 @@ ExecProject(ProjectionInfo *projInfo, bool *isDone)
InvalidBuffer, /* tuple has no buffer */
true);
}