mysql 错误代码： 1248 Every derived table must have its own alias
问题mysql代码：
```
SELECT COUNT(*) FROM (
SELECT cg.`moduleType`,cg.`moduleName` FROM t_category cg GROUP BY cg.`moduleType`,cg.`moduleName`) ;
```
执行之后报错：
```
1 queries executed, 0 success, 1 errors, 0 warnings
查询：select count(*) from ( select cg.`moduleType`,cg.`moduleName` from t_category cg group by cg.`moduleType`,cg.`moduleName`) LIMIT...
错误代码： 1248
Every derived table must have its own alias
```
错误解释：
像是这种多个表联合查询的时候派生出来的表就需要起个别名：
解决办法如下：
```
SELECT COUNT(*) FROM (
SELECT cg.`moduleType`,cg.`moduleName` FROM t_category cg GROUP BY cg.`moduleType`,cg.`moduleName`) a ;
```
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