Various parts of the optimizer create temporary tables for different necessarities. As a result we have similar code in 3 places.
That is create_tmp_table() (and the Create_tmp_table class) in sql_select.cc,
SJ_TMP_TABLE in opt_subselect.cc,
and the Create_json_table class in table_function.cc

It'd be good to unify these three and create the universal Create_tmp_table class to remove code duplications.