Hi Igor, We discussed the problem with error messages with Sergei and both agreed that a new error message like: Subquery is not allowed in '%s' will be more informative, and it's easy to do. Why not replace: bool expr_allows_subselect; to const char *clause_that_disallows_subselect; ? So we can change the grammar to something like this: | opt_generated_always AS { Lex->clause_that_disallows_subselect= "GENERATED ALWAYS AS"; } virtual_column_func { Lex->clause_that_disallows_subselect= NULL; } The same for other places where we disallow subselects. This can be done in 10.4 before your patch, as a separate commit.