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/commands/command.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/Attic/command.c,v 1.169 2002/03/31 06:26:30 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/Attic/command.c,v 1.170 2002/04/01 04:35:38 tgl Exp $
  *
  * NOTES
  *	  The PerformAddAttribute() code, like most of the relation
@@ -403,7 +403,7 @@ AlterTableAddColumn(Oid myrelid,
 
 	if (colDef->is_not_null)
 		elog(ERROR, "Adding NOT NULL columns is not implemented."
-			 "\n\tAdd the column, then use ALTER TABLE ADD CONSTRAINT.");
+			 "\n\tAdd the column, then use ALTER TABLE ... SET NOT NULL.");
 
 	pgclass = heap_openr(RelationRelationName, RowExclusiveLock);
 
@@ -527,6 +527,288 @@ AlterTableAddColumn(Oid myrelid,
 	AlterTableCreateToastTable(myrelid, true);
 }
 
+/*
+ * ALTER TABLE ALTER COLUMN DROP NOT NULL
+ */
+void
+AlterTableAlterColumnDropNotNull(Oid myrelid,
+								 bool inh, const char *colName)
+{
+	Relation	rel;
+	HeapTuple	tuple;
+	AttrNumber	attnum;
+	Relation	attr_rel;
+	List	   	*indexoidlist;
+	List	   	*indexoidscan;
+
+	rel = heap_open(myrelid, AccessExclusiveLock);
+
+	if (rel->rd_rel->relkind != RELKIND_RELATION)
+		elog(ERROR, "ALTER TABLE: relation \"%s\" is not a table",
+			 RelationGetRelationName(rel));
+
+	if (!allowSystemTableMods
+		&& IsSystemRelationName(RelationGetRelationName(rel)))
+		elog(ERROR, "ALTER TABLE: relation \"%s\" is a system catalog",
+			 RelationGetRelationName(rel));
+
+	if (!pg_class_ownercheck(myrelid, GetUserId()))
+		elog(ERROR, "ALTER TABLE: \"%s\": permission denied",
+			 RelationGetRelationName(rel));
+
+	/*
+	 * Propagate to children if desired
+	 */
+	if (inh)
+	{
+		List	   *child,
+				   *children;
+
+		/* this routine is actually in the planner */
+		children = find_all_inheritors(myrelid);
+
+		/*
+		 * find_all_inheritors does the recursive search of the
+		 * inheritance hierarchy, so all we have to do is process all of
+		 * the relids in the list that it returns.
+		 */
+		foreach(child, children)
+		{
+			Oid			childrelid = lfirsti(child);
+
+			if (childrelid == myrelid)
+				continue;
+			AlterTableAlterColumnDropNotNull(childrelid,
+											 false, colName);
+		}
+	}
+
+	/* -= now do the thing on this relation =- */
+
+	/*
+	 * get the number of the attribute
+	 */
+	tuple = SearchSysCache(ATTNAME,
+						   ObjectIdGetDatum(myrelid),
+						   PointerGetDatum(colName),
+						   0, 0);
+	if (!HeapTupleIsValid(tuple))
+		elog(ERROR, "ALTER TABLE: relation \"%s\" has no column \"%s\"",
+			 RelationGetRelationName(rel), colName);
+
+	attnum = ((Form_pg_attribute) GETSTRUCT(tuple))->attnum;
+	ReleaseSysCache(tuple);
+
+	/* Prevent them from altering a system attribute */
+	if (attnum < 0)
+		elog(ERROR, "ALTER TABLE: Cannot alter system attribute \"%s\"",
+			 colName);
+
+	/* 
+	 * Check that the attribute is not in a primary key
+	 */
+		
+	/* Loop over all indices on the relation */
+	indexoidlist = RelationGetIndexList(rel);
+
+	foreach(indexoidscan, indexoidlist)
+	{
+		Oid		indexoid = lfirsti(indexoidscan);
+		HeapTuple	indexTuple;
+		Form_pg_index 	indexStruct;
+		int		i;
+
+		indexTuple = SearchSysCache(INDEXRELID,
+									ObjectIdGetDatum(indexoid),
+									0, 0, 0);
+		if (!HeapTupleIsValid(indexTuple))
+			elog(ERROR, "ALTER TABLE: Index %u not found",
+				 indexoid);
+		indexStruct = (Form_pg_index) GETSTRUCT(indexTuple);
+
+		/* If the index is not a primary key, skip the check */
+		if (indexStruct->indisprimary)
+		{
+			/*
+			 * Loop over each attribute in the primary key and
+			 * see if it matches the to-be-altered attribute
+			 */
+			for (i = 0; i < INDEX_MAX_KEYS &&
+					 indexStruct->indkey[i] != InvalidAttrNumber; i++)
+			{
+				if (indexStruct->indkey[i] == attnum)
+					elog(ERROR, "ALTER TABLE: Attribute \"%s\" is in a primary key", colName);
+			}
+		}
+
+		ReleaseSysCache(indexTuple);
+	}
+
+	freeList(indexoidlist);
+
+	/*
+	 * Okay, actually perform the catalog change
+	 */
+	attr_rel = heap_openr(AttributeRelationName, RowExclusiveLock);
+
+	tuple = SearchSysCacheCopy(ATTNAME,
+							   ObjectIdGetDatum(myrelid),
+							   PointerGetDatum(colName),
+							   0, 0);
+	if (!HeapTupleIsValid(tuple)) /* shouldn't happen */
+		elog(ERROR, "ALTER TABLE: relation \"%s\" has no column \"%s\"",
+			 RelationGetRelationName(rel), colName);
+
+	((Form_pg_attribute) GETSTRUCT(tuple))->attnotnull = FALSE;
+
+	simple_heap_update(attr_rel, &tuple->t_self, tuple);
+
+	/* keep the system catalog indices current */
+	if (RelationGetForm(attr_rel)->relhasindex)
+	{
+		Relation	idescs[Num_pg_attr_indices];
+
+		CatalogOpenIndices(Num_pg_attr_indices, Name_pg_attr_indices, idescs);
+		CatalogIndexInsert(idescs, Num_pg_attr_indices, attr_rel, tuple);
+		CatalogCloseIndices(Num_pg_attr_indices, idescs);
+	}
+
+	heap_close(attr_rel, RowExclusiveLock);
+
+	heap_close(rel, NoLock);
+}
+
+/*
+ * ALTER TABLE ALTER COLUMN SET NOT NULL
+ */
+void
+AlterTableAlterColumnSetNotNull(Oid myrelid,
+								bool inh, const char *colName)
+{
+	Relation	rel;
+	HeapTuple	tuple;
+	AttrNumber	attnum;
+	Relation	attr_rel;
+	HeapScanDesc 	scan;
+	TupleDesc	tupdesc;
+
+	rel = heap_open(myrelid, AccessExclusiveLock);
+
+	if (rel->rd_rel->relkind != RELKIND_RELATION)
+		elog(ERROR, "ALTER TABLE: relation \"%s\" is not a table",
+			 RelationGetRelationName(rel));
+
+	if (!allowSystemTableMods
+		&& IsSystemRelationName(RelationGetRelationName(rel)))
+		elog(ERROR, "ALTER TABLE: relation \"%s\" is a system catalog",
+			 RelationGetRelationName(rel));
+
+	if (!pg_class_ownercheck(myrelid, GetUserId()))
+		elog(ERROR, "ALTER TABLE: \"%s\": permission denied",
+			 RelationGetRelationName(rel));
+
+	/*
+	 * Propagate to children if desired
+	 */
+	if (inh)
+	{
+		List	   *child,
+				   *children;
+
+		/* this routine is actually in the planner */
+		children = find_all_inheritors(myrelid);
+
+		/*
+		 * find_all_inheritors does the recursive search of the
+		 * inheritance hierarchy, so all we have to do is process all of
+		 * the relids in the list that it returns.
+		 */
+		foreach(child, children)
+		{
+			Oid			childrelid = lfirsti(child);
+
+			if (childrelid == myrelid)
+				continue;
+			AlterTableAlterColumnSetNotNull(childrelid,
+											false, colName);
+		}
+	}
+
+	/* -= now do the thing on this relation =- */
+
+	/*
+	 * get the number of the attribute
+	 */
+	tuple = SearchSysCache(ATTNAME,
+						   ObjectIdGetDatum(myrelid),
+						   PointerGetDatum(colName),
+						   0, 0);
+	if (!HeapTupleIsValid(tuple))
+		elog(ERROR, "ALTER TABLE: relation \"%s\" has no column \"%s\"",
+			 RelationGetRelationName(rel), colName);
+
+	attnum = ((Form_pg_attribute) GETSTRUCT(tuple))->attnum;
+	ReleaseSysCache(tuple);
+
+	/* Prevent them from altering a system attribute */
+	if (attnum < 0)
+		elog(ERROR, "ALTER TABLE: Cannot alter system attribute \"%s\"",
+			 colName);
+
+	/*
+	 * Perform a scan to ensure that there are no NULL
+	 * values already in the relation
+	 */
+	tupdesc = RelationGetDescr(rel);
+
+	scan = heap_beginscan(rel, false, SnapshotNow, 0, NULL);
+
+	while (HeapTupleIsValid(tuple = heap_getnext(scan, 0)))
+	{
+		Datum 		d;
+		bool		isnull;
+
+		d = heap_getattr(tuple, attnum, tupdesc, &isnull);
+
+		if (isnull)
+			elog(ERROR, "ALTER TABLE: Attribute \"%s\" contains NULL values",
+				 colName);
+	}
+
+	heap_endscan(scan);
+
+	/*
+	 * Okay, actually perform the catalog change
+	 */
+	attr_rel = heap_openr(AttributeRelationName, RowExclusiveLock);
+
+	tuple = SearchSysCacheCopy(ATTNAME,
+							   ObjectIdGetDatum(myrelid),
+							   PointerGetDatum(colName),
+							   0, 0);
+	if (!HeapTupleIsValid(tuple)) /* shouldn't happen */
+		elog(ERROR, "ALTER TABLE: relation \"%s\" has no column \"%s\"",
+			 RelationGetRelationName(rel), colName);
+
+	((Form_pg_attribute) GETSTRUCT(tuple))->attnotnull = TRUE;
+
+	simple_heap_update(attr_rel, &tuple->t_self, tuple);
+
+	/* keep the system catalog indices current */
+	if (RelationGetForm(attr_rel)->relhasindex)
+	{
+		Relation	idescs[Num_pg_attr_indices];
+
+		CatalogOpenIndices(Num_pg_attr_indices, Name_pg_attr_indices, idescs);
+		CatalogIndexInsert(idescs, Num_pg_attr_indices, attr_rel, tuple);
+		CatalogCloseIndices(Num_pg_attr_indices, idescs);
+	}
+
+	heap_close(attr_rel, RowExclusiveLock);
+
+	heap_close(rel, NoLock);
+}
+
 
 /*
  * ALTER TABLE ALTER COLUMN SET/DROP DEFAULT
@@ -538,7 +820,7 @@ AlterTableAlterColumnDefault(Oid myrelid,
 {
 	Relation	rel;
 	HeapTuple	tuple;
-	int16		attnum;
+	AttrNumber	attnum;
 
 	rel = heap_open(myrelid, AccessExclusiveLock);
 
@@ -552,7 +834,7 @@ AlterTableAlterColumnDefault(Oid myrelid,
 			 RelationGetRelationName(rel));
 
 	if (!pg_class_ownercheck(myrelid, GetUserId()))
-		elog(ERROR, "ALTER TABLE: \"%s\" permission denied",
+		elog(ERROR, "ALTER TABLE: \"%s\": permission denied",
 			 RelationGetRelationName(rel));
 
 	/*
@@ -620,44 +902,36 @@ AlterTableAlterColumnDefault(Oid myrelid,
 	{
 		/* DROP DEFAULT */
 		Relation	attr_rel;
-		ScanKeyData scankeys[3];
-		HeapScanDesc scan;
 
+		/* Fix the pg_attribute row */
 		attr_rel = heap_openr(AttributeRelationName, RowExclusiveLock);
-		ScanKeyEntryInitialize(&scankeys[0], 0x0,
-							   Anum_pg_attribute_attrelid, F_OIDEQ,
-							   ObjectIdGetDatum(myrelid));
-		ScanKeyEntryInitialize(&scankeys[1], 0x0,
-							   Anum_pg_attribute_attnum, F_INT2EQ,
-							   Int16GetDatum(attnum));
-		ScanKeyEntryInitialize(&scankeys[2], 0x0,
-							   Anum_pg_attribute_atthasdef, F_BOOLEQ,
-							   BoolGetDatum(true));
 
-		scan = heap_beginscan(attr_rel, false, SnapshotNow, 3, scankeys);
-		AssertState(scan != NULL);
+		tuple = SearchSysCacheCopy(ATTNAME,
+								   ObjectIdGetDatum(myrelid),
+								   PointerGetDatum(colName),
+								   0, 0);
+		if (!HeapTupleIsValid(tuple)) /* shouldn't happen */
+			elog(ERROR, "ALTER TABLE: relation \"%s\" has no column \"%s\"",
+				 RelationGetRelationName(rel), colName);
 
-		if (HeapTupleIsValid(tuple = heap_getnext(scan, 0)))
-		{
-			HeapTuple	newtuple;
-			Relation	irelations[Num_pg_attr_indices];
+		((Form_pg_attribute) GETSTRUCT(tuple))->atthasdef = FALSE;
 
-			/* update to false */
-			newtuple = heap_copytuple(tuple);
-			((Form_pg_attribute) GETSTRUCT(newtuple))->atthasdef = FALSE;
-			simple_heap_update(attr_rel, &tuple->t_self, newtuple);
+		simple_heap_update(attr_rel, &tuple->t_self, tuple);
 
 		/* keep the system catalog indices current */
-			CatalogOpenIndices(Num_pg_attr_indices, Name_pg_attr_indices, irelations);
-			CatalogIndexInsert(irelations, Num_pg_attr_indices, attr_rel, newtuple);
-			CatalogCloseIndices(Num_pg_attr_indices, irelations);
+		if (RelationGetForm(attr_rel)->relhasindex)
+		{
+			Relation	idescs[Num_pg_attr_indices];
 
-			/* get rid of actual default definition */
-			drop_default(myrelid, attnum);
+			CatalogOpenIndices(Num_pg_attr_indices, Name_pg_attr_indices, idescs);
+			CatalogIndexInsert(idescs, Num_pg_attr_indices, attr_rel, tuple);
+			CatalogCloseIndices(Num_pg_attr_indices, idescs);
 		}
 
-		heap_endscan(scan);
-		heap_close(attr_rel, NoLock);
+		heap_close(attr_rel, RowExclusiveLock);
+
+		/* get rid of actual default definition in pg_attrdef */
+		drop_default(myrelid, attnum);
 	}
 
 	heap_close(rel, NoLock);
@@ -722,7 +996,7 @@ AlterTableAlterColumnFlags(Oid myrelid,
 			 RelationGetRelationName(rel));
 
 	if (!pg_class_ownercheck(myrelid, GetUserId()))
-		elog(ERROR, "ALTER TABLE: \"%s\" permission denied",
+		elog(ERROR, "ALTER TABLE: \"%s\": permission denied",
 			 RelationGetRelationName(rel));
 
 	/*
@@ -1011,7 +1285,7 @@ AlterTableDropColumn(Oid myrelid,
 			 RelationGetRelationName(rel));
 
 	if (!allowSystemTableMods
-		&& IsSystemRelationName(RelationGetRelationName(rel))
+		&& IsSystemRelationName(RelationGetRelationName(rel)))
 		elog(ERROR, "ALTER TABLE: relation \"%s\" is a system catalog",
 			 RelationGetRelationName(rel));
 
@@ -1022,7 +1296,8 @@ AlterTableDropColumn(Oid myrelid,
 	 * normally, only the owner of a class can change its schema.
 	 */
 	if (!pg_class_ownercheck(myrelid, GetUserId()))
-		elog(ERROR, "ALTER TABLE: permission denied");
+		elog(ERROR, "ALTER TABLE: \"%s\": permission denied",
+			 RelationGetRelationName(rel));
 
 	heap_close(rel, NoLock);	/* close rel but keep lock! */
 
@@ -1670,7 +1945,8 @@ AlterTableCreateToastTable(Oid relOid, bool silent)
 			 RelationGetRelationName(rel));
 
 	if (!pg_class_ownercheck(relOid, GetUserId()))
-		elog(ERROR, "ALTER TABLE: permission denied");
+		elog(ERROR, "ALTER TABLE: \"%s\": permission denied",
+			 RelationGetRelationName(rel));
 
 	/*
 	 * lock the pg_class tuple for update (is that really needed?)

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;
+