Every derived table must have its own alias(sql错误)

1. Every derived table must have its own alias 汉语意思为 每个派生表必须有自己的别名.

   原因:
   当我们多表查询时或者出现派生表时可能会出现这样的错误，给表添加一个别名就好了

2. 举例:
   

   在sql语句的结尾给派生表添加一个别名即可
   sql : select count(*) from (select * from mst_object a LEFT JOIN mst_code b on a.OBJ_TYPE=b.CODE where a.PAGE_ID='004' and b.TYPE='005') c (或者 “as c”)