# 案例：改写SQL消除in-clause
#### 现象描述
in-clause/any-clause是常见的SQL语句约束条件，有时in或any后面的clause都是常量，类似于：
```
select count(1) from calc_empfyc_c1_result_tmp_t1 where ls_pid_cusr1 in (‘20120405’, ‘20130405’);
```
或者
```
select count(1) from calc_empfyc_c1_result_tmp_t1 where ls_pid_cusr1 in any(‘20120405’, ‘20130405’);
```
但是也有一些如下的特殊用法：
```
SELECT ls_pid_cusr1,COALESCE(max(round((current_date-bthdate)/365)),0)FROM calc_empfyc_c1_result_tmp_t1 t1,p10_md_tmp_t2 t2WHERE t1.ls_pid_cusr1 = any(values(id),(id15))GROUP BY ls_pid_cusr1;
```
其中，id、id15为p10_md_tmp_t2中的两列，"t1.ls_pid_cusr1 = any(values(id),(id15))"等价于"t1.ls_pid_cusr1 = id or t1.ls_pid_cusr1 = id15"*。*
因此join-condition实质上是一个不等式，这种非等值的join操作必须使用nestloop连接，对应执行计划如下：
![](https://support.huaweicloud.com/distributed-devg-v3-gaussdb/figure/zh-cn_image_0000002235099497.png "点击放大")
#### 优化说明
测试发现由于两表结果集过大，导致nestloop耗时过长，超过一小时未返回结果，因此性能优化的关键是消除nestloop，让join使用更高效的hashjoin。从语义等价的角度消除any-clause，SQL改写如下：
```
selectls_pid_cusr1,COALESCE(max(round(ym/365)),0)from(         (                   SELECT                             ls_pid_cusr1,(current_date-bthdate) as ym                   FROM calc_empfyc_c1_result_tmp_t1 t1,p10_md_tmp_t2 t2                   WHERE t1.ls_pid_cusr1 = t2.id and t1.ls_pid_cusr1 != t2.id15         )         union all         (                   SELECT                             ls_pid_cusr1,(current_date-bthdate) as ym                   FROM calc_empfyc_c1_result_tmp_t1 t1,p10_md_tmp_t2 t2                   WHERE t1.ls_pid_cusr1 = id15         ))GROUP BY ls_pid_cusr1;
```
优化后的SQL查询由两个等值join的子查询构成，而每个子查询都可以走更适合此场景的hashjoin。优化后的执行计划如下
![](https://support.huaweicloud.com/distributed-devg-v3-gaussdb/figure/zh-cn_image_0000002200299200.jpg "点击放大")
优化后，从超过1个小时未返回结果优化到7s返回结果。