# 案例：main plan exec on CN and SubPlan exec on DN can not be shipped
#### 问题根因
根因：复杂语句中的主查询为不涉及用户表的查询，但相关的子查询是涉及用户表的查询语句。
#### 案例1：主查询来源表是维表DUAL
**原始语句**
```
SELECT 
    1 
FROM (SELECT 1 
    FROM dual 
    WHERE -2 = -2
    AND 202210 IN(SELECT /*+ PARALLEL(8) */ 
        DISTINCT PERIOD_ID
        FROM DWICBG_VI.CBGDWR_PSI_FIN_OVER_INV_V T 
        WHERE T.LAST_MODIFIED_DATE > (SELECT NVL(MAX(LAST_MODIFIED_DATE), TRUNC(SYSDATE) - 1) from FIN_DWB_MSS.DWB_MSS_PSI_FIN_OVER_INV_M_F) AND T.LAST_MODIFIED_DATE <= (SELECT  TRUNC(SYSDATE) + 1) 
    )
) t LIMIT 1
```
**改写后语句**
```
SELECT 
    1 
FROM(SELECT 1 
    FROM (SELECT /*+ PARALLEL(8) */
            DISTINCT PERIOD_ID
        FROM DWICBG_VI.CBGDWR_PSI_FIN_OVER_INV_V T 
        WHERE T.LAST_MODIFIED_DATE > (SELECT NVL(MAX(LAST_MODIFIED_DATE), TRUNC(SYSDATE) - 1) from FIN_DWB_MSS.DWB_MSS_PSI_FIN_OVER_INV_M_F) AND T.LAST_MODIFIED_DATE <= (SELECT  TRUNC(SYSDATE) + 1) 
    ) t(PERIOD_ID) 
where PERIOD_ID = 202210
) t LIMIT 1
```
**修改点对比**
![](https://support.huaweicloud.com/devg-911-dws/figure/zh-cn_image_0000002493938586.png "点击放大")