identity-cols.patch

diff --git a/doc/src/sgml/ref/create_table.sgml b/doc/src/sgml/ref/create_table.sgml
new file mode 100644
index 22dbc07..b48a29e
--- a/doc/src/sgml/ref/create_table.sgml
+++ b/doc/src/sgml/ref/create_table.sgml
@@ -803,8 +803,8 @@ WITH ( MODULUS <replaceable class="param
      <para>
       This clause creates the column as an <firstterm>identity
       column</firstterm>.  It will have an implicit sequence attached to it
-      and the column in new rows will automatically have values from the
-      sequence assigned to it.
+      and new rows in the column will automatically have values from the
+      sequence assigned to them.
      </para>
 
      <para>
@@ -815,12 +815,22 @@ WITH ( MODULUS <replaceable class="param
       only accepted if the <command>INSERT</command> statement
       specifies <literal>OVERRIDING SYSTEM VALUE</literal>.  If <literal>BY
       DEFAULT</literal> is specified, then the user-specified value takes
-      precedence.  See <xref linkend="sql-insert"/> for details.  (In
+      precedence, unless the <command>INSERT</command> statement specifies
+      <literal>OVERRIDING USER VALUE</literal>.
+      See <xref linkend="sql-insert"/> for details.  (In
       the <command>COPY</command> command, user-specified values are always
       used regardless of this setting.)
      </para>
 
      <para>
+      Additionally, if <literal>ALWAYS</literal> is specified, any attempt to
+      update the value of the column using an <command>UPDATE</command>
+      statement specifying any value other than <literal>DEFAULT</literal>
+      will be rejected. If <literal>BY DEFAULT</literal> is specified, the
+      system will allow values in the column to be updated.
+     </para>
+
+     <para>
       The optional <replaceable>sequence_options</replaceable> clause can be
       used to override the options of the sequence.
       See <xref linkend="sql-createsequence"/> for details.
diff --git a/doc/src/sgml/ref/insert.sgml b/doc/src/sgml/ref/insert.sgml
new file mode 100644
index 62e142f..8108f31
--- a/doc/src/sgml/ref/insert.sgml
+++ b/doc/src/sgml/ref/insert.sgml
@@ -206,10 +206,16 @@ INSERT INTO <replaceable class="paramete
       <term><literal>OVERRIDING SYSTEM VALUE</literal></term>
       <listitem>
        <para>
-        Without this clause, it is an error to specify an explicit value
-        (other than <literal>DEFAULT</literal>) for an identity column defined
-        as <literal>GENERATED ALWAYS</literal>.  This clause overrides that
-        restriction.
+        If this clause is specified, then any values supplied for identity
+        columns will override the default sequence-generated values.
+       </para>
+
+       <para>
+        For an identity column defined as <literal>GENERATED ALWAYS</literal>,
+        it is an error to insert an explicit value (other than
+        <literal>DEFAULT</literal>) without specifying either
+        <literal>OVERRIDING SYSTEM VALUE</literal> or
+        <literal>OVERRIDING USER VALUE</literal>.
        </para>
       </listitem>
      </varlistentry>
@@ -219,8 +225,8 @@ INSERT INTO <replaceable class="paramete
       <listitem>
        <para>
         If this clause is specified, then any values supplied for identity
-        columns defined as <literal>GENERATED BY DEFAULT</literal> are ignored
-        and the default sequence-generated values are applied.
+        columns are ignored and the default sequence-generated values are
+        applied.
        </para>
 
        <para>
diff --git a/src/backend/rewrite/rewriteHandler.c b/src/backend/rewrite/rewriteHandler.c
new file mode 100644
index 7eb41ff..3dc27eb
--- a/src/backend/rewrite/rewriteHandler.c
+++ b/src/backend/rewrite/rewriteHandler.c
@@ -821,13 +821,15 @@ rewriteTargetListIU(List *targetList,
 		{
 			if (att_tup->attidentity == ATTRIBUTE_IDENTITY_ALWAYS && !apply_default)
 			{
-				if (override != OVERRIDING_SYSTEM_VALUE)
+				if (override == OVERRIDING_USER_VALUE)
+					apply_default = true;
+				else if (override != OVERRIDING_SYSTEM_VALUE)
 					ereport(ERROR,
 							(errcode(ERRCODE_GENERATED_ALWAYS),
 							 errmsg("cannot insert into column \"%s\"", NameStr(att_tup->attname)),
 							 errdetail("Column \"%s\" is an identity column defined as GENERATED ALWAYS.",
 									   NameStr(att_tup->attname)),
-							 errhint("Use OVERRIDING SYSTEM VALUE to override.")));
+							 errhint("You must specify either OVERRIDING SYSTEM VALUE or OVERRIDING USER VALUE.")));
 			}
 
 			if (att_tup->attidentity == ATTRIBUTE_IDENTITY_BY_DEFAULT && override == OVERRIDING_USER_VALUE)
diff --git a/src/test/regress/expected/identity.out b/src/test/regress/expected/identity.out
new file mode 100644
index d7d5178..81044b2
--- a/src/test/regress/expected/identity.out
+++ b/src/test/regress/expected/identity.out
@@ -119,28 +119,32 @@ SELECT * FROM itest3;
 
 -- OVERRIDING tests
 INSERT INTO itest1 VALUES (10, 'xyz');
-INSERT INTO itest1 OVERRIDING USER VALUE VALUES (10, 'xyz');
+INSERT INTO itest1 OVERRIDING SYSTEM VALUE VALUES (20, 'xyz');
+INSERT INTO itest1 OVERRIDING USER VALUE VALUES (30, 'xyz');
 SELECT * FROM itest1;
  a  |  b  
 ----+-----
   1 | 
   2 | 
  10 | xyz
+ 20 | xyz
   3 | xyz
-(4 rows)
+(5 rows)
 
 INSERT INTO itest2 VALUES (10, 'xyz');
 ERROR:  cannot insert into column "a"
 DETAIL:  Column "a" is an identity column defined as GENERATED ALWAYS.
-HINT:  Use OVERRIDING SYSTEM VALUE to override.
-INSERT INTO itest2 OVERRIDING SYSTEM VALUE VALUES (10, 'xyz');
+HINT:  You must specify either OVERRIDING SYSTEM VALUE or OVERRIDING USER VALUE.
+INSERT INTO itest2 OVERRIDING SYSTEM VALUE VALUES (20, 'xyz');
+INSERT INTO itest2 OVERRIDING USER VALUE VALUES (30, 'xyz');
 SELECT * FROM itest2;
  a  |  b  
 ----+-----
   1 | 
   2 | 
- 10 | xyz
-(3 rows)
+ 20 | xyz
+  3 | xyz
+(4 rows)
 
 -- UPDATE tests
 UPDATE itest1 SET a = 101 WHERE a = 1;
@@ -149,10 +153,11 @@ SELECT * FROM itest1;
   a  |  b  
 -----+-----
   10 | xyz
+  20 | xyz
    3 | xyz
  101 | 
    4 | 
-(4 rows)
+(5 rows)
 
 UPDATE itest2 SET a = 101 WHERE a = 1;
 ERROR:  column "a" can only be updated to DEFAULT
@@ -162,9 +167,10 @@ SELECT * FROM itest2;
  a  |  b  
 ----+-----
   1 | 
- 10 | xyz
-  3 | 
-(3 rows)
+ 20 | xyz
+  3 | xyz
+  4 | 
+(4 rows)
 
 -- COPY tests
 CREATE TABLE itest9 (a int GENERATED ALWAYS AS IDENTITY, b text, c bigint);
@@ -240,7 +246,7 @@ SELECT * FROM itestv10;
 INSERT INTO itestv11 VALUES (10, 'xyz');
 ERROR:  cannot insert into column "a"
 DETAIL:  Column "a" is an identity column defined as GENERATED ALWAYS.
-HINT:  Use OVERRIDING SYSTEM VALUE to override.
+HINT:  You must specify either OVERRIDING SYSTEM VALUE or OVERRIDING USER VALUE.
 INSERT INTO itestv11 OVERRIDING SYSTEM VALUE VALUES (11, 'xyz');
 SELECT * FROM itestv11;
  a  |  b  
diff --git a/src/test/regress/sql/identity.sql b/src/test/regress/sql/identity.sql
new file mode 100644
index a35f331..f74353f
--- a/src/test/regress/sql/identity.sql
+++ b/src/test/regress/sql/identity.sql
@@ -65,12 +65,14 @@ SELECT * FROM itest3;
 -- OVERRIDING tests
 
 INSERT INTO itest1 VALUES (10, 'xyz');
-INSERT INTO itest1 OVERRIDING USER VALUE VALUES (10, 'xyz');
+INSERT INTO itest1 OVERRIDING SYSTEM VALUE VALUES (20, 'xyz');
+INSERT INTO itest1 OVERRIDING USER VALUE VALUES (30, 'xyz');
 
 SELECT * FROM itest1;
 
 INSERT INTO itest2 VALUES (10, 'xyz');
-INSERT INTO itest2 OVERRIDING SYSTEM VALUE VALUES (10, 'xyz');
+INSERT INTO itest2 OVERRIDING SYSTEM VALUE VALUES (20, 'xyz');
+INSERT INTO itest2 OVERRIDING USER VALUE VALUES (30, 'xyz');
 
 SELECT * FROM itest2;