COALESCE() and NULLIF() are now first-class expressions, not macros

that turn into CASE expressions.  They evaluate their arguments at most
once.  Patch by Kris Jurka, review and (very light) editorializing by me.

4 files changed, 39 insertions, 6 deletions

diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 8d2b130598..591870be51 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: execnodes.h,v 1.94 2003/02/09 00:30:39 tgl Exp $
+ * $Id: execnodes.h,v 1.95 2003/02/16 02:30:39 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -441,8 +441,9 @@ typedef struct ArrayRefExprState
 /* ----------------
  *		FuncExprState node
  *
- * Although named for FuncExpr, this is also used for OpExpr and DistinctExpr
- * nodes; be careful to check what xprstate.expr is actually pointing at!
+ * Although named for FuncExpr, this is also used for OpExpr, DistinctExpr,
+ * and NullIf nodes; be careful to check what xprstate.expr is actually
+ * pointing at!
  * ----------------
  */
 typedef struct FuncExprState
@@ -540,6 +541,16 @@ typedef struct CaseWhenState
 } CaseWhenState;
 
 /* ----------------
+ *		CoalesceExprState node
+ * ----------------
+ */
+typedef struct CoalesceExprState
+{
+	ExprState	xprstate;
+	List	*args;				/* the arguments */
+} CoalesceExprState;
+
+/* ----------------
  *		CoerceToDomainState node
  * ----------------
  */
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index a218790194..356f4b60fa 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: nodes.h,v 1.136 2003/02/03 21:15:44 tgl Exp $
+ * $Id: nodes.h,v 1.137 2003/02/16 02:30:39 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -112,6 +112,8 @@ typedef enum NodeTag
 	T_RelabelType,
 	T_CaseExpr,
 	T_CaseWhen,
+	T_CoalesceExpr,
+	T_NullIfExpr,
 	T_NullTest,
 	T_BooleanTest,
 	T_CoerceToDomain,
@@ -136,6 +138,7 @@ typedef enum NodeTag
 	T_SubPlanState,
 	T_CaseExprState,
 	T_CaseWhenState,
+	T_CoalesceExprState,
 	T_CoerceToDomainState,
 	T_DomainConstraintState,
 
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 9474bc6490..381c11c389 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: parsenodes.h,v 1.230 2003/02/13 05:20:03 momjian Exp $
+ * $Id: parsenodes.h,v 1.231 2003/02/16 02:30:39 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -174,6 +174,7 @@ typedef enum A_Expr_Kind
 	AEXPR_OR,
 	AEXPR_NOT,
 	AEXPR_DISTINCT,				/* IS DISTINCT FROM - name must be "=" */
+	AEXPR_NULLIF,				/* NULLIF - name must be "=" */
 	AEXPR_OF					/* IS (not) OF - name must be "=" or "!=" */
 } A_Expr_Kind;
 
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index be917c4f26..b8a358d614 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -10,7 +10,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: primnodes.h,v 1.79 2003/02/09 00:30:40 tgl Exp $
+ * $Id: primnodes.h,v 1.80 2003/02/16 02:30:39 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -537,6 +537,24 @@ typedef struct CaseWhen
 	Expr	   *result;			/* substitution result */
 } CaseWhen;
 
+/*
+ * CoalesceExpr - a COALESCE expression
+ */
+typedef struct CoalesceExpr
+{
+	Expr	xpr;
+	Oid		coalescetype;		/* type of expression result */
+	List   *args;				/* the arguments */
+} CoalesceExpr;
+
+/*
+ * NullIfExpr - a NULLIF expression
+ *
+ * Like DistinctExpr, this is represented the same as an OpExpr referencing
+ * the "=" operator for x and y.
+ */
+typedef OpExpr NullIfExpr;
+
 /* ----------------
  * NullTest
  *