Represent BETWEEN as a special node type in raw parse trees.

Previously, gram.y itself converted BETWEEN into AND (or AND/OR) nests of
expression comparisons.  This was always as bogus as could be, but fixing
it hasn't risen to the top of the to-do list.  The present patch invents an
A_Expr representation for BETWEEN expressions, and does the expansion to
comparison trees in parse_expr.c which is at least a slightly saner place
to be doing semantic conversions.  There should be no change in the post-
parse-analysis results.

This does nothing for the semantic issues with BETWEEN (dubious connection
to btree-opclass semantics, and multiple evaluation of possibly volatile
subexpressions) ... but it's a necessary preliminary step before we could
fix any of that.  The main immediate benefit is that preserving BETWEEN as
an identifiable raw-parse-tree construct will enable better error messages.

While at it, fix the code so that multiply-referenced subexpressions are
physically duplicated before being passed through transformExpr().  This
gets rid of one of the principal reasons why transformExpr() has
historically had to allow already-processed input.

src/backend/nodes/outfuncs.c

@@ -2512,6 +2512,22 @@ _outAExpr(StringInfo str, const A_Expr *node)
 			appendStringInfoString(str, " IN ");
 			WRITE_NODE_FIELD(name);
 			break;
+		case AEXPR_BETWEEN:
+			appendStringInfoString(str, " BETWEEN ");
+			WRITE_NODE_FIELD(name);
+			break;
+		case AEXPR_NOT_BETWEEN:
+			appendStringInfoString(str, " NOT_BETWEEN ");
+			WRITE_NODE_FIELD(name);
+			break;
+		case AEXPR_BETWEEN_SYM:
+			appendStringInfoString(str, " BETWEEN_SYM ");
+			WRITE_NODE_FIELD(name);
+			break;
+		case AEXPR_NOT_BETWEEN_SYM:
+			appendStringInfoString(str, " NOT_BETWEEN_SYM ");
+			WRITE_NODE_FIELD(name);
+			break;
 		default:
 			appendStringInfoString(str, " ??");
 			break;

src/backend/parser/gram.y

@@ -11178,7 +11178,7 @@ a_expr:		c_expr									{ $$ = $1; }
 		 * below; and all those operators will have the same precedence.
 		 *
 		 * If you add more explicitly-known operators, be sure to add them
-		 * also to b_expr and to the MathOp list above.
+		 * also to b_expr and to the MathOp list below.
 		 */
 			| '+' a_expr					%prec UMINUS
 				{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "+", NULL, $2, @1); }
@@ -11396,50 +11396,36 @@ a_expr:		c_expr									{ $$ = $1; }
 				{
 					$$ = (Node *) makeSimpleA_Expr(AEXPR_OF, "<>", $1, (Node *) $6, @2);
 				}
-			/*
-			 *	Ideally we would not use hard-wired operators below but
-			 *	instead use opclasses.  However, mixed data types and other
-			 *	issues make this difficult:
-			 *	http://archives.postgresql.org/pgsql-hackers/2008-08/msg01142.php
-			 */
 			| a_expr BETWEEN opt_asymmetric b_expr AND b_expr		%prec BETWEEN
 				{
-					$$ = makeAndExpr(
-						(Node *) makeSimpleA_Expr(AEXPR_OP, ">=", $1, $4, @2),
-						(Node *) makeSimpleA_Expr(AEXPR_OP, "<=", $1, $6, @2),
+					$$ = (Node *) makeSimpleA_Expr(AEXPR_BETWEEN,
+												   "BETWEEN",
+												   $1,
+												   (Node *) list_make2($4, $6),
 												   @2);
 				}
 			| a_expr NOT BETWEEN opt_asymmetric b_expr AND b_expr	%prec BETWEEN
 				{
-					$$ = makeOrExpr(
-						(Node *) makeSimpleA_Expr(AEXPR_OP, "<", $1, $5, @2),
-						(Node *) makeSimpleA_Expr(AEXPR_OP, ">", $1, $7, @2),
+					$$ = (Node *) makeSimpleA_Expr(AEXPR_NOT_BETWEEN,
+												   "NOT BETWEEN",
+												   $1,
+												   (Node *) list_make2($5, $7),
 												   @2);
 				}
 			| a_expr BETWEEN SYMMETRIC b_expr AND b_expr			%prec BETWEEN
 				{
-					$$ = makeOrExpr(
-						  makeAndExpr(
-							(Node *) makeSimpleA_Expr(AEXPR_OP, ">=", $1, $4, @2),
-							(Node *) makeSimpleA_Expr(AEXPR_OP, "<=", $1, $6, @2),
-									  @2),
-						  makeAndExpr(
-							(Node *) makeSimpleA_Expr(AEXPR_OP, ">=", $1, $6, @2),
-							(Node *) makeSimpleA_Expr(AEXPR_OP, "<=", $1, $4, @2),
-									  @2),
+					$$ = (Node *) makeSimpleA_Expr(AEXPR_BETWEEN_SYM,
+												   "BETWEEN SYMMETRIC",
+												   $1,
+												   (Node *) list_make2($4, $6),
 												   @2);
 				}
 			| a_expr NOT BETWEEN SYMMETRIC b_expr AND b_expr		%prec BETWEEN
 				{
-					$$ = makeAndExpr(
-						   makeOrExpr(
-							(Node *) makeSimpleA_Expr(AEXPR_OP, "<", $1, $5, @2),
-							(Node *) makeSimpleA_Expr(AEXPR_OP, ">", $1, $7, @2),
-									  @2),
-						   makeOrExpr(
-							(Node *) makeSimpleA_Expr(AEXPR_OP, "<", $1, $7, @2),
-							(Node *) makeSimpleA_Expr(AEXPR_OP, ">", $1, $5, @2),
-									  @2),
+					$$ = (Node *) makeSimpleA_Expr(AEXPR_NOT_BETWEEN_SYM,
+												   "NOT BETWEEN SYMMETRIC",
+												   $1,
+												   (Node *) list_make2($5, $7),
 												   @2);
 				}
 			| a_expr IN_P in_expr

src/backend/parser/parse_expr.c

@@ -48,6 +48,7 @@ static Node *transformAExprDistinct(ParseState *pstate, A_Expr *a);
 static Node *transformAExprNullIf(ParseState *pstate, A_Expr *a);
 static Node *transformAExprOf(ParseState *pstate, A_Expr *a);
 static Node *transformAExprIn(ParseState *pstate, A_Expr *a);
+static Node *transformAExprBetween(ParseState *pstate, A_Expr *a);
 static Node *transformBoolExpr(ParseState *pstate, BoolExpr *a);
 static Node *transformFuncCall(ParseState *pstate, FuncCall *fn);
 static Node *transformMultiAssignRef(ParseState *pstate, MultiAssignRef *maref);
@@ -241,6 +242,12 @@ transformExprRecurse(ParseState *pstate, Node *expr)
 					case AEXPR_IN:
 						result = transformAExprIn(pstate, a);
 						break;
+					case AEXPR_BETWEEN:
+					case AEXPR_NOT_BETWEEN:
+					case AEXPR_BETWEEN_SYM:
+					case AEXPR_NOT_BETWEEN_SYM:
+						result = transformAExprBetween(pstate, a);
+						break;
 					default:
 						elog(ERROR, "unrecognized A_Expr kind: %d", a->kind);
 						result = NULL;	/* keep compiler quiet */
@@ -1195,6 +1202,101 @@ transformAExprIn(ParseState *pstate, A_Expr *a)
 	return result;
 }
 
+static Node *
+transformAExprBetween(ParseState *pstate, A_Expr *a)
+{
+	Node	   *aexpr;
+	Node	   *bexpr;
+	Node	   *cexpr;
+	Node	   *result;
+	Node	   *sub1;
+	Node	   *sub2;
+	List	   *args;
+
+	/* Deconstruct A_Expr into three subexprs */
+	aexpr = a->lexpr;
+	Assert(IsA(a->rexpr, List));
+	args = (List *) a->rexpr;
+	Assert(list_length(args) == 2);
+	bexpr = (Node *) linitial(args);
+	cexpr = (Node *) lsecond(args);
+
+	/*
+	 * Build the equivalent comparison expression.  Make copies of
+	 * multiply-referenced subexpressions for safety.  (XXX this is really
+	 * wrong since it results in multiple runtime evaluations of what may be
+	 * volatile expressions ...)
+	 *
+	 * Ideally we would not use hard-wired operators here but instead use
+	 * opclasses.  However, mixed data types and other issues make this
+	 * difficult:
+	 * http://archives.postgresql.org/pgsql-hackers/2008-08/msg01142.php
+	 */
+	switch (a->kind)
+	{
+		case AEXPR_BETWEEN:
+			args = list_make2(makeSimpleA_Expr(AEXPR_OP, ">=",
+											   aexpr, bexpr,
+											   a->location),
+							  makeSimpleA_Expr(AEXPR_OP, "<=",
+											   copyObject(aexpr), cexpr,
+											   a->location));
+			result = (Node *) makeBoolExpr(AND_EXPR, args, a->location);
+			break;
+		case AEXPR_NOT_BETWEEN:
+			args = list_make2(makeSimpleA_Expr(AEXPR_OP, "<",
+											   aexpr, bexpr,
+											   a->location),
+							  makeSimpleA_Expr(AEXPR_OP, ">",
+											   copyObject(aexpr), cexpr,
+											   a->location));
+			result = (Node *) makeBoolExpr(OR_EXPR, args, a->location);
+			break;
+		case AEXPR_BETWEEN_SYM:
+			args = list_make2(makeSimpleA_Expr(AEXPR_OP, ">=",
+											   aexpr, bexpr,
+											   a->location),
+							  makeSimpleA_Expr(AEXPR_OP, "<=",
+											   copyObject(aexpr), cexpr,
+											   a->location));
+			sub1 = (Node *) makeBoolExpr(AND_EXPR, args, a->location);
+			args = list_make2(makeSimpleA_Expr(AEXPR_OP, ">=",
+										copyObject(aexpr), copyObject(cexpr),
+											   a->location),
+							  makeSimpleA_Expr(AEXPR_OP, "<=",
+										copyObject(aexpr), copyObject(bexpr),
+											   a->location));
+			sub2 = (Node *) makeBoolExpr(AND_EXPR, args, a->location);
+			args = list_make2(sub1, sub2);
+			result = (Node *) makeBoolExpr(OR_EXPR, args, a->location);
+			break;
+		case AEXPR_NOT_BETWEEN_SYM:
+			args = list_make2(makeSimpleA_Expr(AEXPR_OP, "<",
+											   aexpr, bexpr,
+											   a->location),
+							  makeSimpleA_Expr(AEXPR_OP, ">",
+											   copyObject(aexpr), cexpr,
+											   a->location));
+			sub1 = (Node *) makeBoolExpr(OR_EXPR, args, a->location);
+			args = list_make2(makeSimpleA_Expr(AEXPR_OP, "<",
+										copyObject(aexpr), copyObject(cexpr),
+											   a->location),
+							  makeSimpleA_Expr(AEXPR_OP, ">",
+										copyObject(aexpr), copyObject(bexpr),
+											   a->location));
+			sub2 = (Node *) makeBoolExpr(OR_EXPR, args, a->location);
+			args = list_make2(sub1, sub2);
+			result = (Node *) makeBoolExpr(AND_EXPR, args, a->location);
+			break;
+		default:
+			elog(ERROR, "unrecognized A_Expr kind: %d", a->kind);
+			result = NULL;		/* keep compiler quiet */
+			break;
+	}
+
+	return transformExprRecurse(pstate, result);
+}
+
 static Node *
 transformBoolExpr(ParseState *pstate, BoolExpr *a)
 {

src/include/nodes/parsenodes.h

@@ -232,7 +232,11 @@ typedef enum A_Expr_Kind
 	AEXPR_DISTINCT,				/* IS DISTINCT FROM - name must be "=" */
 	AEXPR_NULLIF,				/* NULLIF - name must be "=" */
 	AEXPR_OF,					/* IS [NOT] OF - name must be "=" or "<>" */
-	AEXPR_IN					/* [NOT] IN - name must be "=" or "<>" */
+	AEXPR_IN,					/* [NOT] IN - name must be "=" or "<>" */
+	AEXPR_BETWEEN,				/* name must be "BETWEEN" */
+	AEXPR_NOT_BETWEEN,			/* name must be "NOT BETWEEN" */
+	AEXPR_BETWEEN_SYM,			/* name must be "BETWEEN SYMMETRIC" */
+	AEXPR_NOT_BETWEEN_SYM		/* name must be "NOT BETWEEN SYMMETRIC" */
 } A_Expr_Kind;
 
 typedef struct A_Expr