Allow ALTER VIEW command to rename the column in the view.

ALTER TABLE RENAME COLUMN command always can be used to rename the column
in the view, but it's reasonable to add that syntax to ALTER VIEW too.

Author: Fujii Masao
Reviewed-by: Ibrar Ahmed, Yu Kimura
Discussion: https://postgr.es/m/CAHGQGwHoQMD3b-MqTLcp1MgdhCpOKU7QNRwjFooT4_d+ti5v6g@mail.gmail.com

doc/src/sgml/ref/alter_view.sgml

@@ -24,6 +24,7 @@ PostgreSQL documentation
 ALTER VIEW [ IF EXISTS ] <replaceable class="parameter">name</replaceable> ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET DEFAULT <replaceable class="parameter">expression</replaceable>
 ALTER VIEW [ IF EXISTS ] <replaceable class="parameter">name</replaceable> ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> DROP DEFAULT
 ALTER VIEW [ IF EXISTS ] <replaceable class="parameter">name</replaceable> OWNER TO { <replaceable class="parameter">new_owner</replaceable> | CURRENT_USER | SESSION_USER }
+ALTER VIEW [ IF EXISTS ] <replaceable class="parameter">name</replaceable> RENAME [ COLUMN ] <replaceable class="parameter">column_name</replaceable> TO <replaceable class="parameter">new_column_name</replaceable>
 ALTER VIEW [ IF EXISTS ] <replaceable class="parameter">name</replaceable> RENAME TO <replaceable class="parameter">new_name</replaceable>
 ALTER VIEW [ IF EXISTS ] <replaceable class="parameter">name</replaceable> SET SCHEMA <replaceable class="parameter">new_schema</replaceable>
 ALTER VIEW [ IF EXISTS ] <replaceable class="parameter">name</replaceable> SET ( <replaceable class="parameter">view_option_name</replaceable> [= <replaceable class="parameter">view_option_value</replaceable>] [, ... ] )
@@ -65,6 +66,24 @@ ALTER VIEW [ IF EXISTS ] <replaceable class="parameter">name</replaceable> RESET
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><replaceable class="parameter">column_name</replaceable></term>
+    <listitem>
+     <para>
+      Name of an existing column.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">new_column_name</replaceable></term>
+    <listitem>
+     <para>
+      New name for an existing column.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>IF EXISTS</literal></term>
     <listitem>

src/backend/commands/view.c

@@ -276,7 +276,8 @@ checkViewTupleDesc(TupleDesc newdesc, TupleDesc olddesc)
 					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
 					 errmsg("cannot change name of view column \"%s\" to \"%s\"",
 							NameStr(oldattr->attname),
-							NameStr(newattr->attname))));
+							NameStr(newattr->attname)),
+					 errhint("Use ALTER VIEW ... RENAME COLUMN ... to change name of view column instead.")));
 		/* XXX would it be safe to allow atttypmod to change?  Not sure */
 		if (newattr->atttypid != oldattr->atttypid ||
 			newattr->atttypmod != oldattr->atttypmod)

src/backend/parser/gram.y

@@ -8777,6 +8777,28 @@ RenameStmt: ALTER AGGREGATE aggregate_with_argtypes RENAME TO name
 					n->missing_ok = true;
 					$$ = (Node *)n;
 				}
+			| ALTER VIEW qualified_name RENAME opt_column name TO name
+				{
+					RenameStmt *n = makeNode(RenameStmt);
+					n->renameType = OBJECT_COLUMN;
+					n->relationType = OBJECT_VIEW;
+					n->relation = $3;
+					n->subname = $6;
+					n->newname = $8;
+					n->missing_ok = false;
+					$$ = (Node *)n;
+				}
+			| ALTER VIEW IF_P EXISTS qualified_name RENAME opt_column name TO name
+				{
+					RenameStmt *n = makeNode(RenameStmt);
+					n->renameType = OBJECT_COLUMN;
+					n->relationType = OBJECT_VIEW;
+					n->relation = $5;
+					n->subname = $8;
+					n->newname = $10;
+					n->missing_ok = true;
+					$$ = (Node *)n;
+				}
 			| ALTER MATERIALIZED VIEW qualified_name RENAME opt_column name TO name
 				{
 					RenameStmt *n = makeNode(RenameStmt);

src/bin/psql/tab-complete.c

@@ -1797,8 +1797,20 @@ psql_completion(const char *text, int start, int end)
 		COMPLETE_WITH("TO");
 	/* ALTER VIEW <name> */
 	else if (Matches("ALTER", "VIEW", MatchAny))
-		COMPLETE_WITH("ALTER COLUMN", "OWNER TO", "RENAME TO",
+		COMPLETE_WITH("ALTER COLUMN", "OWNER TO", "RENAME",
 					  "SET SCHEMA");
+	/* ALTER VIEW xxx RENAME */
+	else if (Matches("ALTER", "VIEW", MatchAny, "RENAME"))
+		COMPLETE_WITH_ATTR(prev2_wd, " UNION SELECT 'COLUMN' UNION SELECT 'TO'");
+	else if (Matches("ALTER", "VIEW", MatchAny, "ALTER|RENAME", "COLUMN"))
+		COMPLETE_WITH_ATTR(prev3_wd, "");
+	/* ALTER VIEW xxx RENAME yyy */
+	else if (Matches("ALTER", "VIEW", MatchAny, "RENAME", MatchAnyExcept("TO")))
+		COMPLETE_WITH("TO");
+	/* ALTER VIEW xxx RENAME COLUMN yyy */
+	else if (Matches("ALTER", "VIEW", MatchAny, "RENAME", "COLUMN", MatchAnyExcept("TO")))
+		COMPLETE_WITH("TO");
+
 	/* ALTER MATERIALIZED VIEW <name> */
 	else if (Matches("ALTER", "MATERIALIZED", "VIEW", MatchAny))
 		COMPLETE_WITH("ALTER COLUMN", "CLUSTER ON", "DEPENDS ON EXTENSION",

src/test/regress/expected/create_view.out

@@ -64,6 +64,7 @@ ERROR:  cannot drop columns from view
 CREATE OR REPLACE VIEW viewtest AS
 	SELECT 1, * FROM viewtest_tbl;
 ERROR:  cannot change name of view column "a" to "?column?"
+HINT:  Use ALTER VIEW ... RENAME COLUMN ... to change name of view column instead.
 -- should fail
 CREATE OR REPLACE VIEW viewtest AS
 	SELECT a, b::numeric FROM viewtest_tbl;
@@ -1189,6 +1190,29 @@ select pg_get_viewdef('vv1', true);
       CROSS JOIN tt6) j(aa, bb, cc_1, cc, dd);
 (1 row)
 
+create view v4 as select * from v1;
+alter view v1 rename column a to x;
+select pg_get_viewdef('v1', true);
+                  pg_get_viewdef                   
+---------------------------------------------------
+  SELECT tt2.b,                                   +
+     tt3.c,                                       +
+     tt2.a AS x,                                  +
+     tt3.ax                                       +
+    FROM tt2                                      +
+      JOIN tt3 tt3(ax, b, c, c_1, e) USING (b, c);
+(1 row)
+
+select pg_get_viewdef('v4', true);
+ pg_get_viewdef 
+----------------
+  SELECT v1.b, +
+     v1.c,     +
+     v1.x AS a,+
+     v1.ax     +
+    FROM v1;
+(1 row)
+
 -- Unnamed FULL JOIN USING is lots of fun too
 create table tt7 (x int, xx int, y int);
 alter table tt7 drop column xx;
@@ -1782,7 +1806,7 @@ drop cascades to view aliased_view_2
 drop cascades to view aliased_view_3
 drop cascades to view aliased_view_4
 DROP SCHEMA testviewschm2 CASCADE;
-NOTICE:  drop cascades to 63 other objects
+NOTICE:  drop cascades to 64 other objects
 DETAIL:  drop cascades to table t1
 drop cascades to view temporal1
 drop cascades to view temporal2
@@ -1818,6 +1842,7 @@ drop cascades to view v3
 drop cascades to table tt5
 drop cascades to table tt6
 drop cascades to view vv1
+drop cascades to view v4
 drop cascades to table tt7
 drop cascades to table tt8
 drop cascades to view vv2

src/test/regress/sql/create_view.sql

@@ -391,6 +391,12 @@ select pg_get_viewdef('vv1', true);
 alter table tt5 drop column c;
 select pg_get_viewdef('vv1', true);
 
+create view v4 as select * from v1;
+alter view v1 rename column a to x;
+select pg_get_viewdef('v1', true);
+select pg_get_viewdef('v4', true);
+
+
 -- Unnamed FULL JOIN USING is lots of fun too
 
 create table tt7 (x int, xx int, y int);