Add Oracle-compatible GREATEST and LEAST functions. Pavel Stehule

Author: tglsfdc

doc/src/sgml/func.sgml

@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.259 2005/06/24 20:53:29 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.260 2005/06/26 22:05:35 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -6901,6 +6901,39 @@ SELECT NULLIF(value, '(none)') ...
 
   </sect2>
 
+  <sect2>
+   <title><literal>GREATEST</literal> and <literal>LEAST</literal></title>
+
+  <indexterm>
+   <primary>GREATEST</primary>
+  </indexterm>
+  <indexterm>
+   <primary>LEAST</primary>
+  </indexterm>
+
+<synopsis>
+<function>GREATEST</function>(<replaceable>value</replaceable> <optional>, ...</optional>)
+</synopsis>
+<synopsis>
+<function>LEAST</function>(<replaceable>value</replaceable> <optional>, ...</optional>)
+</synopsis>
+
+   <para>
+    The <function>GREATEST</> and <function>LEAST</> functions select the
+    largest or smallest value from a list of any number of expressions.
+    The expressions must all be convertible to a common data type, which
+    will be the type of the result
+    (see <xref linkend="typeconv-union-case"> for details).  NULL values
+    in the list are ignored.  The result will be NULL only if all the
+    expressions evaluate to NULL.
+   </para>
+
+   <para>
+    Note that <function>GREATEST</> and <function>LEAST</> are not in
+    the SQL standard, but are a common extension.
+   </para>
+  </sect2>
+
  </sect1>
 
 

doc/src/sgml/typeconv.sgml

@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/typeconv.sgml,v 1.43 2004/12/23 23:07:38 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/typeconv.sgml,v 1.44 2005/06/26 22:05:36 tgl Exp $
 -->
 
 <chapter Id="typeconv">
@@ -120,7 +120,7 @@ with, and perhaps converted to, the types of the target columns.
 </varlistentry>
 <varlistentry>
 <term>
-<literal>UNION</literal>, <literal>CASE</literal>, and <literal>ARRAY</literal> constructs
+<literal>UNION</literal>, <literal>CASE</literal>, and related constructs
 </term>
 <listitem>
 <para>
@@ -129,7 +129,8 @@ must appear in a single set of columns, the types of the results of each
 <command>SELECT</> clause must be matched up and converted to a uniform set.
 Similarly, the result expressions of a <literal>CASE</> construct must be
 converted to a common type so that the <literal>CASE</> expression as a whole
-has a known output type.  The same holds for <literal>ARRAY</> constructs.
+has a known output type.  The same holds for <literal>ARRAY</> constructs,
+and for the <function>GREATEST</> and <function>LEAST</> functions.
 </para>
 </listitem>
 </varlistentry>
@@ -782,7 +783,7 @@ padding spaces.
 </sect1>
 
 <sect1 id="typeconv-union-case">
-<title><literal>UNION</literal>, <literal>CASE</literal>, and <literal>ARRAY</literal> Constructs</title>
+<title><literal>UNION</literal>, <literal>CASE</literal>, and Related Constructs</title>
 
 <indexterm zone="typeconv-union-case">
  <primary>UNION</primary>
@@ -799,20 +800,31 @@ padding spaces.
  <secondary>determination of result type</secondary>
 </indexterm>
 
+<indexterm zone="typeconv-union-case">
+ <primary>GREATEST</primary>
+ <secondary>determination of result type</secondary>
+</indexterm>
+
+<indexterm zone="typeconv-union-case">
+ <primary>LEAST</primary>
+ <secondary>determination of result type</secondary>
+</indexterm>
+
 <para>
 SQL <literal>UNION</> constructs must match up possibly dissimilar
 types to become a single result set.  The resolution algorithm is
 applied separately to each output column of a union query.  The
 <literal>INTERSECT</> and <literal>EXCEPT</> constructs resolve
 dissimilar types in the same way as <literal>UNION</>.  The
-<literal>CASE</> and <literal>ARRAY</> constructs use the identical
+<literal>CASE</>, <literal>ARRAY</>, <function>GREATEST</> and
+<function>LEAST</> constructs use the identical
 algorithm to match up their component expressions and select a result
 data type.
 </para>
 
 <procedure>
-<title><literal>UNION</literal>, <literal>CASE</literal>, and
-<literal>ARRAY</literal> Type Resolution</title>
+<title>Type Resolution for <literal>UNION</literal>, <literal>CASE</literal>,
+and Related Constructs</title>
 
 <step performance="required">
 <para>

src/backend/executor/execQual.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.179 2005/05/12 20:41:56 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.180 2005/06/26 22:05:36 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -105,6 +105,9 @@ static Datum ExecEvalRow(RowExprState *rstate,
 static Datum ExecEvalCoalesce(CoalesceExprState *coalesceExpr,
 				 ExprContext *econtext,
 				 bool *isNull, ExprDoneCond *isDone);
+static Datum ExecEvalMinMax(MinMaxExprState *minmaxExpr,
+							ExprContext *econtext,
+							bool *isNull, ExprDoneCond *isDone);
 static Datum ExecEvalNullIf(FuncExprState *nullIfExpr,
 			   ExprContext *econtext,
 			   bool *isNull, ExprDoneCond *isDone);
@@ -2247,6 +2250,63 @@ ExecEvalCoalesce(CoalesceExprState *coalesceExpr, ExprContext *econtext,
 	return (Datum) 0;
 }
 
+/* ----------------------------------------------------------------
+ *		ExecEvalMinMax
+ * ----------------------------------------------------------------
+ */
+static Datum
+ExecEvalMinMax(MinMaxExprState *minmaxExpr, ExprContext *econtext,
+			   bool *isNull, ExprDoneCond *isDone)
+{
+	Datum result = (Datum) 0;
+	MinMaxOp	op = ((MinMaxExpr *) minmaxExpr->xprstate.expr)->op;
+	FunctionCallInfoData locfcinfo;
+	ListCell *arg;
+
+	if (isDone)
+		*isDone = ExprSingleResult;
+	*isNull = true;				/* until we get a result */
+
+	InitFunctionCallInfoData(locfcinfo, &minmaxExpr->cfunc, 2, NULL, NULL);
+	locfcinfo.argnull[0] = false;
+	locfcinfo.argnull[1] = false;
+
+	foreach(arg, minmaxExpr->args)
+	{
+		ExprState  *e = (ExprState *) lfirst(arg);
+		Datum		value;
+		bool		valueIsNull;
+		int32		cmpresult;
+
+		value = ExecEvalExpr(e, econtext, &valueIsNull, NULL);
+		if (valueIsNull)
+			continue;			/* ignore NULL inputs */
+
+		if (*isNull)
+		{
+			/* first nonnull input, adopt value */
+			result = value;
+			*isNull = false;
+		}
+		else
+		{
+			/* apply comparison function */
+			locfcinfo.arg[0] = result;
+			locfcinfo.arg[1] = value;
+			locfcinfo.isnull = false;
+			cmpresult = DatumGetInt32(FunctionCallInvoke(&locfcinfo));
+			if (locfcinfo.isnull) /* probably should not happen */
+				continue;
+			if (cmpresult > 0 && op == IS_LEAST)
+				result = value;
+			else if (cmpresult < 0 && op == IS_GREATEST)
+				result = value;
+		}
+	}
+
+	return result;
+}
+
 /* ----------------------------------------------------------------
  *		ExecEvalNullIf
  *
@@ -3206,6 +3266,36 @@ ExecInitExpr(Expr *node, PlanState *parent)
 				state = (ExprState *) cstate;
 			}
 			break;
+		case T_MinMaxExpr:
+			{
+				MinMaxExpr *minmaxexpr = (MinMaxExpr *) node;
+				MinMaxExprState *mstate = makeNode(MinMaxExprState);
+				List	   *outlist = NIL;
+				ListCell   *l;
+				TypeCacheEntry *typentry;
+
+				mstate->xprstate.evalfunc = (ExprStateEvalFunc) ExecEvalMinMax;
+				foreach(l, minmaxexpr->args)
+				{
+					Expr	   *e = (Expr *) lfirst(l);
+					ExprState  *estate;
+
+					estate = ExecInitExpr(e, parent);
+					outlist = lappend(outlist, estate);
+				}
+				mstate->args = outlist;
+				/* Look up the btree comparison function for the datatype */
+				typentry = lookup_type_cache(minmaxexpr->minmaxtype,
+											 TYPECACHE_CMP_PROC);
+				if (!OidIsValid(typentry->cmp_proc))
+					ereport(ERROR,
+							(errcode(ERRCODE_UNDEFINED_FUNCTION),
+							 errmsg("could not identify a comparison function for type %s",
+									format_type_be(minmaxexpr->minmaxtype))));
+				fmgr_info(typentry->cmp_proc, &(mstate->cfunc));
+				state = (ExprState *) mstate;
+			}
+			break;
 		case T_NullIfExpr:
 			{
 				NullIfExpr *nullifexpr = (NullIfExpr *) node;

src/backend/nodes/copyfuncs.c

@@ -15,7 +15,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/copyfuncs.c,v 1.308 2005/06/22 21:14:29 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/copyfuncs.c,v 1.309 2005/06/26 22:05:37 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1047,6 +1047,21 @@ _copyCoalesceExpr(CoalesceExpr *from)
 	return newnode;
 }
 
+/*
+ * _copyMinMaxExpr
+ */
+static MinMaxExpr *
+_copyMinMaxExpr(MinMaxExpr *from)
+{
+	MinMaxExpr *newnode = makeNode(MinMaxExpr);
+
+	COPY_SCALAR_FIELD(minmaxtype);
+	COPY_SCALAR_FIELD(op);
+	COPY_NODE_FIELD(args);
+
+	return newnode;
+}
+
 /*
  * _copyNullIfExpr (same as OpExpr)
  */
@@ -2805,6 +2820,9 @@ copyObject(void *from)
 		case T_CoalesceExpr:
 			retval = _copyCoalesceExpr(from);
 			break;
+		case T_MinMaxExpr:
+			retval = _copyMinMaxExpr(from);
+			break;
 		case T_NullIfExpr:
 			retval = _copyNullIfExpr(from);
 			break;

src/backend/nodes/equalfuncs.c

@@ -18,7 +18,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/equalfuncs.c,v 1.245 2005/06/22 21:14:29 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/equalfuncs.c,v 1.246 2005/06/26 22:05:37 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -450,6 +450,16 @@ _equalCoalesceExpr(CoalesceExpr *a, CoalesceExpr *b)
 	return true;
 }
 
+static bool
+_equalMinMaxExpr(MinMaxExpr *a, MinMaxExpr *b)
+{
+	COMPARE_SCALAR_FIELD(minmaxtype);
+	COMPARE_SCALAR_FIELD(op);
+	COMPARE_NODE_FIELD(args);
+
+	return true;
+}
+
 static bool
 _equalNullIfExpr(NullIfExpr *a, NullIfExpr *b)
 {
@@ -1868,6 +1878,9 @@ equal(void *a, void *b)
 		case T_CoalesceExpr:
 			retval = _equalCoalesceExpr(a, b);
 			break;
+		case T_MinMaxExpr:
+			retval = _equalMinMaxExpr(a, b);
+			break;
 		case T_NullIfExpr:
 			retval = _equalNullIfExpr(a, b);
 			break;

src/backend/nodes/outfuncs.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.255 2005/06/09 04:18:58 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.256 2005/06/26 22:05:37 tgl Exp $
  *
  * NOTES
  *	  Every node type that can appear in stored rules' parsetrees *must*
@@ -864,6 +864,16 @@ _outCoalesceExpr(StringInfo str, CoalesceExpr *node)
 	WRITE_NODE_FIELD(args);
 }
 
+static void
+_outMinMaxExpr(StringInfo str, MinMaxExpr *node)
+{
+	WRITE_NODE_TYPE("MINMAX");
+
+	WRITE_OID_FIELD(minmaxtype);
+	WRITE_ENUM_FIELD(op, MinMaxOp);
+	WRITE_NODE_FIELD(args);
+}
+
 static void
 _outNullIfExpr(StringInfo str, NullIfExpr *node)
 {
@@ -1896,6 +1906,9 @@ _outNode(StringInfo str, void *obj)
 			case T_CoalesceExpr:
 				_outCoalesceExpr(str, obj);
 				break;
+			case T_MinMaxExpr:
+				_outMinMaxExpr(str, obj);
+				break;
 			case T_NullIfExpr:
 				_outNullIfExpr(str, obj);
 				break;

src/backend/nodes/readfuncs.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/readfuncs.c,v 1.178 2005/06/05 22:32:54 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/readfuncs.c,v 1.179 2005/06/26 22:05:37 tgl Exp $
  *
  * NOTES
  *	  Path and Plan nodes do not have any readfuncs support, because we
@@ -658,6 +658,21 @@ _readCoalesceExpr(void)
 	READ_DONE();
 }
 
+/*
+ * _readMinMaxExpr
+ */
+static MinMaxExpr *
+_readMinMaxExpr(void)
+{
+	READ_LOCALS(MinMaxExpr);
+
+	READ_OID_FIELD(minmaxtype);
+	READ_ENUM_FIELD(op, MinMaxOp);
+	READ_NODE_FIELD(args);
+
+	READ_DONE();
+}
+
 /*
  * _readNullIfExpr
  */
@@ -982,6 +997,8 @@ parseNodeString(void)
 		return_value = _readRowExpr();
 	else if (MATCH("COALESCE", 8))
 		return_value = _readCoalesceExpr();
+	else if (MATCH("MINMAX", 6))
+		return_value = _readMinMaxExpr();
 	else if (MATCH("NULLIFEXPR", 10))
 		return_value = _readNullIfExpr();
 	else if (MATCH("NULLTEST", 8))