Hello, Sergei! Looks fine for me. So if you both prefer it more, let's use this variant.
Regards, Nikita On Wed, Jul 28, 2021 at 12:08 PM Sergei Golubchik <[email protected]> wrote: > Hi, Nikita! > > On Jul 27, Nikita Malyavin wrote: > > revision-id: ce289840131 (mariadb-10.3.30-31-gce289840131) > > parent(s): b50ea900636 > > author: Nikita Malyavin > > committer: Nikita Malyavin > > timestamp: 2021-07-22 22:38:31 +0300 > > message: > > > > MDEV-24511 null field is created with CREATE..SELECT > > > > The regression has been initially appeared by MDEV-12588 patch > (441349aa). > > > > The reason CREATE... SELECT NULL does not create null field is that > > it calls handle_select(), where the field is created directly from Item, > > by calling type_handler->type_handler_for_tmp_table(), instead of plain > > type_handler. > > > > In UNION case, we'll already have Item_field's containing UNION'ed tmp > > table fields to the moment of select_create::prepare() call. > > > > There, item's type_handler is used directly in > > st_select_lex_unit::join_union_item_types(), instead of > > type_handler_for_tmp_table() or type_handler_for_union(). > > > > Using those two involve too many changes in CREATE...SELECT...UNION > > behavior, which may be reasonably undesired to be pushed in 10.3 > > > > However, patching Field_null::type_handler() directly seems to be > accurate > > enough. > > > > diff --git a/mysql-test/main/union.result b/mysql-test/main/union.result > > index a892f6c9e40..b19427948a6 100644 > > --- a/mysql-test/main/union.result > > +++ b/mysql-test/main/union.result > > @@ -1609,7 +1609,7 @@ NULL binary(0) YES NULL > > CREATE TABLE t5 SELECT NULL UNION SELECT NULL; > > DESC t5; > > Field Type Null Key Default Extra > > -NULL null YES NULL > > +NULL binary(0) YES NULL > > CREATE TABLE t6 > > SELECT * FROM (SELECT * FROM (SELECT NULL)a) b UNION SELECT a FROM t1; > > DESC t6; > > diff --git a/sql/field.h b/sql/field.h > > index a3385736c0a..2af5346bea9 100644 > > --- a/sql/field.h > > +++ b/sql/field.h > > @@ -2526,7 +2526,7 @@ class Field_null :public Field_str { > > :Field_str(ptr_arg, len_arg, null, 1, > > unireg_check_arg, field_name_arg, collation) > > {} > > - const Type_handler *type_handler() const { return &type_handler_null; > } > > + const Type_handler *type_handler() const { return > &type_handler_string; } > > Information_schema_character_attributes > > information_schema_character_attributes() const > > { > > This looks suspiciously risky to me. The problem was specifically in > UNION, but you change the very basic idea of what type the Field_null > is. > > I cannot clearly see what else might this possibly affect, field's type > is used everywhere. > > It would be safer and more logical to fix specifically field creation > for UNION. > > I've discussed it with Bar, who implemented this whole Type_handler > hierarchy, he suggested to use Type_handler::union_element_finalize() > for that. I've attached the patch that does that. > > union_element_finalize() is for 10.4, so I also backported it to 10.3, > it's very straightforward though. > > What do you think? > > Regards, > Sergei > VP of MariaDB Server Engineering > and [email protected] > -- Nikita Malyavin, Software Engineer MariaDB Corporation
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