SQL Standards starting from SQL-1999 uses the construct <table value constructor> as
one of the alternatives for <simple table>:
Currently MariaDB uses <table value constructor> only in insert statements:
With <table value constructor> it will be possible to use such CTE specification:
Now instead of this we have to use something like this:
Processing of the latter will take much more memory.
Besides with the possibility of using table value constructors in CTE specifications some optimization transformations for IN predicates will be possible.