mysql数据库delete语句不支持别名，用表名代替别名引用

delete数据时，不支持表别名
如：delete from test a;
[Err] 1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'a' at line 1

当必须用表别名来过滤时，可用表名代替表别名
如：delete from test where exists(select b.id from test2 b where b.id=test.id);