3 files changed, 33 insertions, 1 deletions
diff --git a/src/backend/parser/parse_utilcmd.c b/src/backend/parser/parse_utilcmd.c
index 6e1093a858d..7cf5944ab37 100644
--- a/src/backend/parser/parse_utilcmd.c
+++ b/src/backend/parser/parse_utilcmd.c
@@ -728,7 +728,17 @@ transformColumnDefinition(CreateStmtContext *cxt, ColumnDef *column)
 
 					column->identity = constraint->generated_when;
 					saw_identity = true;
-					column->is_not_null = TRUE;
+
+					/* An identity column is implicitly NOT NULL */
+					if (saw_nullable && !column->is_not_null)
+						ereport(ERROR,
+								(errcode(ERRCODE_SYNTAX_ERROR),
+								 errmsg("conflicting NULL/NOT NULL declarations for column \"%s\" of table \"%s\"",
+										column->colname, cxt->relation->relname),
+								 parser_errposition(cxt->pstate,
+													constraint->location)));
+					column->is_not_null = true;
+					saw_nullable = true;
 					break;
 				}
 
diff --git a/src/test/regress/expected/identity.out b/src/test/regress/expected/identity.out
index 3562cd4f68a..374807cc94f 100644
--- a/src/test/regress/expected/identity.out
+++ b/src/test/regress/expected/identity.out
@@ -386,3 +386,16 @@ CREATE TABLE itest_child PARTITION OF itest_parent (
 ) FOR VALUES FROM ('2016-07-01') TO ('2016-08-01'); -- error
 ERROR:  identity columns are not supported on partitions
 DROP TABLE itest_parent;
+-- Identity columns must be NOT NULL (cf bug #16913)
+CREATE TABLE itest15 (id integer GENERATED ALWAYS AS IDENTITY NULL); -- fail
+ERROR:  conflicting NULL/NOT NULL declarations for column "id" of table "itest15"
+LINE 1: ...ABLE itest15 (id integer GENERATED ALWAYS AS IDENTITY NULL);
+                                                                 ^
+CREATE TABLE itest15 (id integer NULL GENERATED ALWAYS AS IDENTITY); -- fail
+ERROR:  conflicting NULL/NOT NULL declarations for column "id" of table "itest15"
+LINE 1: CREATE TABLE itest15 (id integer NULL GENERATED ALWAYS AS ID...
+                                              ^
+CREATE TABLE itest15 (id integer GENERATED ALWAYS AS IDENTITY NOT NULL);
+DROP TABLE itest15;
+CREATE TABLE itest15 (id integer NOT NULL GENERATED ALWAYS AS IDENTITY);
+DROP TABLE itest15;
diff --git a/src/test/regress/sql/identity.sql b/src/test/regress/sql/identity.sql
index e3459be497a..d71a2a4d498 100644
--- a/src/test/regress/sql/identity.sql
+++ b/src/test/regress/sql/identity.sql
@@ -246,3 +246,12 @@ CREATE TABLE itest_child PARTITION OF itest_parent (
     f3 WITH OPTIONS GENERATED ALWAYS AS IDENTITY
 ) FOR VALUES FROM ('2016-07-01') TO ('2016-08-01'); -- error
 DROP TABLE itest_parent;
+
+-- Identity columns must be NOT NULL (cf bug #16913)
+
+CREATE TABLE itest15 (id integer GENERATED ALWAYS AS IDENTITY NULL); -- fail
+CREATE TABLE itest15 (id integer NULL GENERATED ALWAYS AS IDENTITY); -- fail
+CREATE TABLE itest15 (id integer GENERATED ALWAYS AS IDENTITY NOT NULL);
+DROP TABLE itest15;
+CREATE TABLE itest15 (id integer NOT NULL GENERATED ALWAYS AS IDENTITY);
+DROP TABLE itest15;