Fix for bug #14693 (ALTER COLUMN SET DEFAULT has no effect)

mysql-test/r/alter_table.result:
  test result
mysql-test/t/alter_table.test:
  test case
sql/sql_table.cc:
  we should set the flag with the ALTER requirements

mysql-test/r/alter_table.result

@@ -556,3 +556,9 @@ ERROR 3D000: No database selected
 alter table test.t1 rename test.t1;
 use test;
 drop table t1;
+create table t1 (mycol int(10) not null);
+alter table t1 alter column mycol set default 0;
+desc t1;
+Field	Type	Null	Key	Default	Extra
+mycol	int(10)	NO		0	
+drop table t1;

mysql-test/t/alter_table.test

@@ -401,3 +401,12 @@ use test;
 drop table t1;
 
 # End of 4.1 tests
+
+#
+# Bug #14693 (ALTER SET DEFAULT doesn't work)
+#
+
+create table t1 (mycol int(10) not null);
+alter table t1 alter column mycol set default 0;
+desc t1;
+drop table t1;

sql/sql_table.cc

@@ -3379,7 +3379,10 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
 	  my_error(ER_BLOB_CANT_HAVE_DEFAULT, MYF(0), def->change);
 	  DBUG_RETURN(TRUE);
 	}
-	def->def=alter->def;			// Use new default
+	if ((def->def=alter->def))              // Use new default
+          def->flags&= ~NO_DEFAULT_VALUE_FLAG;
+        else
+          def->flags|= NO_DEFAULT_VALUE_FLAG;
 	alter_it.remove();
       }
     }