MDEV-30007 SIGSEGV in st_select_lex_unit::is_derived_eliminated, runtime error: member access within null pointer of type 'struct TABLE' in st_select_lex_unit::is_derived_eliminated()

Take into account case of a degenerate subquery (like SELECT 1).

followup for 57d233e2

update libmariadb

It looks like  C/C reconnect retains the database. It is correct behavior
However there is a problem that mysql_install_db.exe does not create
'test' database, thus using mysql_install_db to create datadir,
then restarting server and reconnecting does not succeed, if 'test' was
current db before reconnect.

The problem became apparent with MDEV-26715. Why it worked before,
with a simpler 'root' definition is a mystery.

Fix is to switch current connection to 'mysql' database, prior to
reconnect to the instance created via mysql_install_db.exe

Allow passwordless login in addition to usual login with password, when
creating 'root' user during install.

The effect of that change is that "local administrators" group are
allowed to connect as root user. This is done via gssapi authentication
plugin.

Clients that are not aware of gssapi client plugin, can still login with
password credentials.

Make sure that EXPLAIN object allocated on runtime arena.

from mysql-test-run.

it's now redundant

print PUBLIC not quoted in SHOW GRANTS, PUBLIC is not a role

* "public" should work in any letter case
* PUBLIC is not a valid definer
* granting to public should auto-create an entry in mysql.global_priv
* SHOW GRANTS should show privileges obtained via PUBLIC
* LEX_USER::is_public was often uninitialized
* comments, whitespaces, typos, etc

MDEV-5215 prerequisite of prerequisite: if DB is not mentioned in connect ignore errors of switching to it

MDEV-29924 Assertion `(((nr) % (1LL << 24)) % (int) log_10_int[6 - dec]) == 0' failed in my_time_packed_to_binary on SELECT when using TIME field

when assigning the cached item to the Item_cache for the first time
make sure to use Item_cache::setup(), not Item_cache::store().
Because the former copies the metadata (and allocates memory, in case
of Item_cache_row), and Item_cache::decimal must be set for
comparisons to work correctly.

Revert "MDEV-27233 Server hangs when using --init-file which loads Spider and creates a Spider table"

This reverts commit c160a115.

also call top_level_transform() recursively for

(a OR b) AND (c OR d)