Bug#12518

  "COLUMN_DEFAULT has wrong value if NOT NULL is set"
  Show NULL instead of empty string when no default value is set

mysql-test/r/information_schema.result

@@ -958,3 +958,12 @@ trigger_schema	trigger_name
 test	tr1
 use test;
 drop table t1;
+create table t1 (a int not null, b int);
+use information_schema;
+select column_name, column_default from columns
+where table_schema='test' and table_name='t1';
+column_name	column_default
+a	NULL
+b	NULL
+use test;
+drop table t1;

mysql-test/t/information_schema.test

@@ -639,3 +639,13 @@ select trigger_schema, trigger_name from triggers where
 trigger_name='tr1';
 use test;
 drop table t1;
+
+#
+# Bug#12518 COLUMN_DEFAULT has wrong value if NOT NULL is set
+#
+create table t1 (a int not null, b int);
+use information_schema;
+select column_name, column_default from columns
+  where table_schema='test' and table_name='t1';
+use test;
+drop table t1;

sql/sql_show.cc

@@ -2462,6 +2462,7 @@ static int get_schema_column_record(THD *thd, struct st_table_list *tables,
         table->field[5]->set_notnull();
       }
       else if (field->unireg_check == Field::NEXT_NUMBER ||
+               lex->orig_sql_command != SQLCOM_SHOW_FIELDS ||
                field->maybe_null())
         table->field[5]->set_null();                // Null as default
       else