[feature] support SHOW FULL COLUMNS

[andyli029]

Summary

Already supported：SHOW COLUMNS
need support：SHOW FULL COLUMNS

mysql> SHOW FULL COLUMNS FROM `wubx`;
ERROR 1149 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use, syntax error at position 18 near 'columns'
mysql> SHOW COLUMNS FROM `wubx`;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| ID    | int(11)     | YES  |     | NULL    |       |
| a     | int(11)     | NO   | PRI | NULL    |       |
| b     | varchar(25) | YES  |     | NULL    |       |
| c     | int(11)     | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+

[zhyass]

SHOW [FULL] {COLUMNS | FIELDS} 
FROM tbl_name
[LIKE 'pattern' | WHERE expr]