From 511977144dfe5db1208d2e57ac03b95b7e9a1e6e Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: Tue, 24 Mar 2015 10:24:11 -0300
Subject: [PATCH 03/37] deparse/core: transform expr during parse analysis in
 ALTER COLUMN TYPE

... instead of doing it during the execution phase.
---
 src/backend/commands/tablecmds.c   | 39 +++++++++----------------------------
 src/backend/parser/parse_utilcmd.c | 40 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+), 30 deletions(-)

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index e29b2c0..47d5d3b 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -7770,7 +7770,7 @@ ATPrepAlterColumnType(List **wqueue,
 	char	   *colName = cmd->name;
 	ColumnDef  *def = (ColumnDef *) cmd->def;
 	TypeName   *typeName = def->typeName;
-	Node	   *transform = def->raw_default;
+	Node	   *transform;
 	HeapTuple	tuple;
 	Form_pg_attribute attTup;
 	AttrNumber	attnum;
@@ -7829,32 +7829,16 @@ ATPrepAlterColumnType(List **wqueue,
 	{
 		/*
 		 * Set up an expression to transform the old data value to the new
-		 * type. If a USING option was given, transform and use that
-		 * expression, else just take the old value and try to coerce it.  We
-		 * do this first so that type incompatibility can be detected before
-		 * we waste effort, and because we need the expression to be parsed
-		 * against the original table row type.
+		 * type. If a USING option was given, use the expression as transformed
+		 * by transformAlterTableStmt, else just take the old value and try to
+		 * coerce it.  We do this first so that type incompatibility can be
+		 * detected before we waste effort, and because we need the expression
+		 * to be parsed against the original table row type.
 		 */
-		if (transform)
+		if (def->cooked_default)
 		{
-			RangeTblEntry *rte;
-
-			/* Expression must be able to access vars of old table */
-			rte = addRangeTableEntryForRelation(pstate,
-												rel,
-												NULL,
-												false,
-												true);
-			addRTEtoQuery(pstate, rte, false, true, true);
-
-			transform = transformExpr(pstate, transform,
-									  EXPR_KIND_ALTER_COL_TRANSFORM);
-
-			/* It can't return a set */
-			if (expression_returns_set(transform))
-				ereport(ERROR,
-						(errcode(ERRCODE_DATATYPE_MISMATCH),
-					  errmsg("transform expression must not return a set")));
+			/* transformAlterTableStmt already did the work */
+			transform = def->cooked_default;
 		}
 		else
 		{
@@ -7895,11 +7879,6 @@ ATPrepAlterColumnType(List **wqueue,
 		if (ATColumnChangeRequiresRewrite(transform, attnum))
 			tab->rewrite |= AT_REWRITE_COLUMN_REWRITE;
 	}
-	else if (transform)
-		ereport(ERROR,
-				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-				 errmsg("\"%s\" is not a table",
-						RelationGetRelationName(rel))));
 
 	if (tab->relkind == RELKIND_COMPOSITE_TYPE ||
 		tab->relkind == RELKIND_FOREIGN_TABLE)
diff --git a/src/backend/parser/parse_utilcmd.c b/src/backend/parser/parse_utilcmd.c
index 1bbed95..0fa6285 100644
--- a/src/backend/parser/parse_utilcmd.c
+++ b/src/backend/parser/parse_utilcmd.c
@@ -2372,6 +2372,7 @@ transformAlterTableStmt(Oid relid, AlterTableStmt *stmt,
 	List	   *newcmds = NIL;
 	bool		skipValidation = true;
 	AlterTableCmd *newcmd;
+	RangeTblEntry *rte;
 
 	/*
 	 * We must not scribble on the passed-in AlterTableStmt, so copy it. (This
@@ -2411,6 +2412,13 @@ transformAlterTableStmt(Oid relid, AlterTableStmt *stmt,
 	cxt.alist = NIL;
 	cxt.pkey = NULL;
 
+	rte = addRangeTableEntryForRelation(pstate,
+										rel,
+										NULL,
+										false,
+										true);
+	addRTEtoQuery(pstate, rte, false, true, true);
+
 	/*
 	 * The only subtypes that currently require parse transformation handling
 	 * are ADD COLUMN and ADD CONSTRAINT.  These largely re-use code from
@@ -2446,6 +2454,38 @@ transformAlterTableStmt(Oid relid, AlterTableStmt *stmt,
 					newcmds = lappend(newcmds, cmd);
 					break;
 				}
+			case AT_AlterColumnType:
+				{
+					ColumnDef *def = (ColumnDef *) cmd->def;
+
+					/*
+					 * For ALTER COLUMN TYPE, transform the USING clause if
+					 * one was specified.
+					 */
+					if (def->raw_default)
+					{
+						/* USING is only valid for plain tables */
+						if (rel->rd_rel->relkind != RELKIND_RELATION)
+							ereport(ERROR,
+									(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+									 errmsg("\"%s\" is not a table",
+											RelationGetRelationName(rel))));
+
+						def->cooked_default =
+							transformExpr(pstate, def->raw_default,
+										  EXPR_KIND_ALTER_COL_TRANSFORM);
+
+						/* it can't return a set */
+						if (expression_returns_set(def->cooked_default))
+							ereport(ERROR,
+									(errcode(ERRCODE_DATATYPE_MISMATCH),
+									 errmsg("transform expression must not return a set")));
+					}
+
+					newcmds = lappend(newcmds, cmd);
+					break;
+				}
+
 			case AT_AddConstraint:
 
 				/*
-- 
2.1.4