ddl: show create table for a local temporary table

[djshow832]

A subtask of #24169.

[zhaoxugang]

/assign

[tiancaiamao]

mysql> create temporary table tmp1 (id int primary key, u int unique, v int);
Query OK, 0 rows affected (0.00 sec)

mysql> show create table tmp1;
ERROR 1105 (HY000): runtime error: invalid memory address or nil pointer dereference