ALTER TABLE SET/DROP NOT NULL, from Christopher Kings-Lynne.

doc/src/sgml/ref/alter_table.sgml

 <!--
-$Header: /cvsroot/pgsql/doc/src/sgml/ref/alter_table.sgml,v 1.40 2002/03/06 20:42:38 momjian Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/ref/alter_table.sgml,v 1.41 2002/04/01 04:35:37 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -28,6 +28,8 @@ ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> [ * ]
 ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> [ * ]
     ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> { SET DEFAULT <replaceable
     class="PARAMETER">value</replaceable> | DROP DEFAULT }
+ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> [ * ]
+    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> { SET | DROP } NOT NULL
 ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> [ * ]
     ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> SET STATISTICS <replaceable class="PARAMETER">integer</replaceable>
 ALTER TABLE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> [ * ]
@@ -168,6 +170,9 @@ ALTER TABLE <replaceable class="PARAMETER">table</replaceable>
    allow you to set or remove the default for the column. Note that defaults
    only apply to subsequent <command>INSERT</command> commands; they do not
    cause rows already in the table to change.
+   The <literal>ALTER COLUMN SET/DROP NOT NULL</literal> forms allow you to
+   change whether a column is marked to allow NULL values or to reject NULL
+   values.
    The <literal>ALTER COLUMN SET STATISTICS</literal> form allows you to
    set the statistics-gathering target for subsequent
    <xref linkend="sql-analyze" endterm="sql-analyze-title"> operations.
@@ -279,6 +284,17 @@ ALTER TABLE distributors RENAME TO suppliers;
    </programlisting>
   </para>
 
+  <para>
+   To add a NOT NULL constraint to a column:
+   <programlisting>
+ALTER TABLE distributors ALTER COLUMN street SET NOT NULL;
+   </programlisting>
+   To remove a NOT NULL constraint from a column:
+   <programlisting>
+ALTER TABLE distributors ALTER COLUMN street DROP NOT NULL;
+   </programlisting>
+  </para>
+
   <para> 
    To add a check constraint to a table:
    <programlisting>

doc/src/sgml/release.sgml

 <!--
-$Header: /cvsroot/pgsql/doc/src/sgml/release.sgml,v 1.128 2002/03/25 21:24:08 momjian Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/release.sgml,v 1.129 2002/04/01 04:35:37 tgl Exp $
 -->
 
 <appendix id="release">
@@ -24,6 +24,7 @@ CDATA means the content is "SGML-free", so you can write without
 worries about funny characters.
 -->
 <literallayout><![CDATA[
+ALTER TABLE ALTER COLUMN SET/DROP NOT NULL
 EXPLAIN output comes out as a query result, not a NOTICE message
 DOMAINs (types that are constrained versions of base types)
 Access privileges on functions

src/backend/parser/gram.y

@@ -11,7 +11,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/parser/gram.y,v 2.298 2002/04/01 03:34:25 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/parser/gram.y,v 2.299 2002/04/01 04:35:38 tgl Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -1122,6 +1122,24 @@ AlterTableStmt:
 					n->def = $7;
 					$$ = (Node *)n;
 				}
+/* ALTER TABLE <relation> ALTER [COLUMN] <colname> DROP NOT NULL */
+                | ALTER TABLE relation_expr ALTER opt_column ColId DROP NOT NULL_P
+                                {
+                                        AlterTableStmt *n = makeNode(AlterTableStmt);
+                                        n->subtype = 'N';
+                                        n->relation = $3;
+                                        n->name = $6;
+                                        $$ = (Node *)n;
+                                }
+/* ALTER TABLE <relation> ALTER [COLUMN] <colname> SET NOT NULL */
+                | ALTER TABLE relation_expr ALTER opt_column ColId SET NOT NULL_P
+                                {
+                                        AlterTableStmt *n = makeNode(AlterTableStmt);
+                                        n->subtype = 'O';
+                                        n->relation = $3;
+                                        n->name = $6;
+                                        $$ = (Node *)n;
+                                }
 /* ALTER TABLE <relation> ALTER [COLUMN] <colname> SET STATISTICS <Iconst> */
 		| ALTER TABLE relation_expr ALTER opt_column ColId SET STATISTICS Iconst
 				{

src/backend/tcop/utility.c

@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/tcop/utility.c,v 1.144 2002/03/31 07:49:30 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/tcop/utility.c,v 1.145 2002/04/01 04:35:39 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -437,6 +437,16 @@ ProcessUtility(Node *parsetree,
 													 stmt->name,
 													 stmt->def);
 						break;
+					case 'N':	/* ALTER COLUMN DROP NOT NULL */
+						AlterTableAlterColumnDropNotNull(RangeVarGetRelid(stmt->relation, false),
+										interpretInhOption(stmt->relation->inhOpt),
+													stmt->name);
+						break;
+					case 'O':	/* ALTER COLUMN SET NOT NULL */
+						AlterTableAlterColumnSetNotNull(RangeVarGetRelid(stmt->relation, false),
+										interpretInhOption(stmt->relation->inhOpt),
+													stmt->name);
+						break;
 					case 'S':	/* ALTER COLUMN STATISTICS */
 					case 'M':   /* ALTER COLUMN STORAGE */
 						/*

src/include/commands/command.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: command.h,v 1.36 2002/03/29 19:06:21 tgl Exp $
+ * $Id: command.h,v 1.37 2002/04/01 04:35:39 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -45,6 +45,12 @@ extern void AlterTableAddColumn(Oid myrelid, bool inherits, ColumnDef *colDef);
 extern void AlterTableAlterColumnDefault(Oid myrelid, bool inh,
 										 const char *colName, Node *newDefault);
 
+extern void AlterTableAlterColumnDropNotNull(Oid myrelid,
+							 bool inh, const char *colName);
+
+extern void AlterTableAlterColumnSetNotNull(Oid myrelid,
+							 bool inh, const char *colName);
+
 extern void AlterTableAlterColumnFlags(Oid myrelid,
 									   bool inh, const char *colName,
 									   Node *flagValue, const char *flagType);

src/include/nodes/parsenodes.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: parsenodes.h,v 1.166 2002/03/29 19:06:23 tgl Exp $
+ * $Id: parsenodes.h,v 1.167 2002/04/01 04:35:40 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -728,6 +728,8 @@ typedef struct AlterTableStmt
 	char		subtype;		/*------------
 								 *	A = add column
 								 *	T = alter column default
+								 *	N = alter column drop not null
+								 *	O = alter column set not null
 								 *	S = alter column statistics
 								 *  M = alter column storage
 								 *	D = drop column

src/test/regress/expected/alter_table.out

@@ -578,3 +578,74 @@ ERROR:  Cannot insert a duplicate key into unique index atacc1_pkey
 insert into atacc1 (test2, test) values (1, NULL);
 ERROR:  ExecAppend: Fail to add null value in not null attribute test
 drop table atacc1;
+-- alter table / alter column [set/drop] not null tests
+-- try altering system catalogs, should fail
+alter table pg_class alter column relname drop not null;
+ERROR:  ALTER TABLE: relation "pg_class" is a system catalog
+alter table pg_class alter relname set not null;
+ERROR:  ALTER TABLE: relation "pg_class" is a system catalog
+-- try altering non-existent table, should fail
+alter table foo alter column bar set not null;
+ERROR:  Relation "foo" does not exist
+alter table foo alter column bar drop not null;
+ERROR:  Relation "foo" does not exist
+-- test setting columns to null and not null and vice versa
+-- test checking for null values and primary key
+create table atacc1 (test int not null);
+alter table atacc1 add constraint "atacc1_pkey" primary key (test);
+NOTICE:  ALTER TABLE / ADD PRIMARY KEY will create implicit index 'atacc1_pkey' for table 'atacc1'
+alter table atacc1 alter column test drop not null;
+ERROR:  ALTER TABLE: Attribute "test" is in a primary key
+drop index atacc1_pkey;
+alter table atacc1 alter column test drop not null;
+insert into atacc1 values (null);
+alter table atacc1 alter test set not null;
+ERROR:  ALTER TABLE: Attribute "test" contains NULL values
+delete from atacc1;
+alter table atacc1 alter test set not null;
+-- try altering a non-existent column, should fail
+alter table atacc1 alter bar set not null;
+ERROR:  ALTER TABLE: relation "atacc1" has no column "bar"
+alter table atacc1 alter bar drop not null;
+ERROR:  ALTER TABLE: relation "atacc1" has no column "bar"
+-- try altering the oid column, should fail
+alter table atacc1 alter oid set not null;
+ERROR:  ALTER TABLE: Cannot alter system attribute "oid"
+alter table atacc1 alter oid drop not null;
+ERROR:  ALTER TABLE: Cannot alter system attribute "oid"
+-- try creating a view and altering that, should fail
+create view myview as select * from atacc1;
+alter table myview alter column test drop not null;
+ERROR:  ALTER TABLE: relation "myview" is not a table
+alter table myview alter column test set not null;
+ERROR:  ALTER TABLE: relation "myview" is not a table
+drop view myview;
+drop table atacc1;
+-- test inheritance
+create table parent (a int);
+create table child (b varchar(255)) inherits (parent);
+alter table parent alter a set not null;
+insert into parent values (NULL);
+ERROR:  ExecAppend: Fail to add null value in not null attribute a
+insert into child (a, b) values (NULL, 'foo');
+ERROR:  ExecAppend: Fail to add null value in not null attribute a
+alter table parent alter a drop not null;
+insert into parent values (NULL);
+insert into child (a, b) values (NULL, 'foo');
+alter table only parent alter a set not null;
+ERROR:  ALTER TABLE: Attribute "a" contains NULL values
+alter table child alter a set not null;
+ERROR:  ALTER TABLE: Attribute "a" contains NULL values
+delete from parent;
+alter table only parent alter a set not null;
+insert into parent values (NULL);
+ERROR:  ExecAppend: Fail to add null value in not null attribute a
+alter table child alter a set not null;
+insert into child (a, b) values (NULL, 'foo');
+ERROR:  ExecAppend: Fail to add null value in not null attribute a
+delete from child;
+alter table child alter a set not null;
+insert into child (a, b) values (NULL, 'foo');
+ERROR:  ExecAppend: Fail to add null value in not null attribute a
+drop table child;
+drop table parent;

src/test/regress/sql/alter_table.sql

@@ -452,3 +452,64 @@ insert into atacc1 (test2, test) values (3, 3);
 insert into atacc1 (test2, test) values (2, 3);
 insert into atacc1 (test2, test) values (1, NULL);
 drop table atacc1;
+
+-- alter table / alter column [set/drop] not null tests
+-- try altering system catalogs, should fail
+alter table pg_class alter column relname drop not null;
+alter table pg_class alter relname set not null;
+
+-- try altering non-existent table, should fail
+alter table foo alter column bar set not null;
+alter table foo alter column bar drop not null;
+
+-- test setting columns to null and not null and vice versa
+-- test checking for null values and primary key
+create table atacc1 (test int not null);
+alter table atacc1 add constraint "atacc1_pkey" primary key (test);
+alter table atacc1 alter column test drop not null;
+drop index atacc1_pkey;
+alter table atacc1 alter column test drop not null;
+insert into atacc1 values (null);
+alter table atacc1 alter test set not null;
+delete from atacc1;
+alter table atacc1 alter test set not null;
+
+-- try altering a non-existent column, should fail
+alter table atacc1 alter bar set not null;
+alter table atacc1 alter bar drop not null;
+
+-- try altering the oid column, should fail
+alter table atacc1 alter oid set not null;
+alter table atacc1 alter oid drop not null;
+
+-- try creating a view and altering that, should fail
+create view myview as select * from atacc1;
+alter table myview alter column test drop not null;
+alter table myview alter column test set not null;
+drop view myview;
+
+drop table atacc1;
+
+-- test inheritance
+create table parent (a int);
+create table child (b varchar(255)) inherits (parent);
+
+alter table parent alter a set not null;
+insert into parent values (NULL);
+insert into child (a, b) values (NULL, 'foo');
+alter table parent alter a drop not null;
+insert into parent values (NULL);
+insert into child (a, b) values (NULL, 'foo');
+alter table only parent alter a set not null;
+alter table child alter a set not null;
+delete from parent;
+alter table only parent alter a set not null;
+insert into parent values (NULL);
+alter table child alter a set not null;
+insert into child (a, b) values (NULL, 'foo');
+delete from child;
+alter table child alter a set not null;
+insert into child (a, b) values (NULL, 'foo');
+drop table child;
+drop table parent;
+