# 案例：增加JOIN列非空条件
#### 现象描述
```
SELECT
 * 
FROM
( ( SELECT
  STARTTIME STTIME,
  SUM(NVL(PAGE_DELAY_MSEL,0)) PAGE_DELAY_MSEL,
  SUM(NVL(PAGE_SUCCEED_TIMES,0)) PAGE_SUCCEED_TIMES,
  SUM(NVL(FST_PAGE_REQ_NUM,0)) FST_PAGE_REQ_NUM,
  SUM(NVL(PAGE_AVG_SIZE,0)) PAGE_AVG_SIZE,
  SUM(NVL(FST_PAGE_ACK_NUM,0)) FST_PAGE_ACK_NUM,
  SUM(NVL(DATATRANS_DW_DURATION,0)) DATATRANS_DW_DURATION,
  SUM(NVL(PAGE_SR_DELAY_MSEL,0)) PAGE_SR_DELAY_MSEL 
 FROM
  PS.SDR_WEB_BSCRNC_1DAY SDR
  INNER JOIN (SELECT
      BSCRNC_ID,
      BSCRNC_NAME,
      ACCESS_TYPE,
      ACCESS_TYPE_ID 
     FROM
      nethouse.DIM_LOC_BSCRNC 
     GROUP BY
      BSCRNC_ID,
      BSCRNC_NAME,
      ACCESS_TYPE,
      ACCESS_TYPE_ID) DIM 
  ON SDR.BSCRNC_ID = DIM.BSCRNC_ID 
  AND DIM.ACCESS_TYPE_ID IN (0,1,2) 
  INNER JOIN nethouse.DIM_RAT_MAPPING RAT 
  ON (RAT.RAT = SDR.RAT)
 WHERE
  ( (STARTTIME >= 1461340800 
  AND STARTTIME < 1461427200) ) 
  AND RAT.ACCESS_TYPE_ID IN (0,1,2) 
  --and SDR.BSCRNC_ID is not null
 GROUP BY
  STTIME ) ) ;
```
执行计划如[图1]所示。
图1增加JOIN列非空条件（一）   
![](https://support.huaweicloud.com/distributed-devg-v2-gaussdb/figure/zh-cn_image_0000002220899277.jpg "点击放大")
#### 优化分析
1. 分析执行计划[图1]可知，在顺序扫描阶段耗时较多。
2. 多表JOIN中，由于表PS.SDR_WEB_BSCRNC_1DAY的JOIN列"BSCRNC_ID"存在大量空值，JOIN性能差。 建议在语句中手动添加JOIN列的非空判断，修改后的语句如下所示。
   ```
   SELECT
    * 
   FROM
   ( ( SELECT
     STARTTIME STTIME,
     SUM(NVL(PAGE_DELAY_MSEL,0)) PAGE_DELAY_MSEL,
     SUM(NVL(PAGE_SUCCEED_TIMES,0)) PAGE_SUCCEED_TIMES,
     SUM(NVL(FST_PAGE_REQ_NUM,0)) FST_PAGE_REQ_NUM,
     SUM(NVL(PAGE_AVG_SIZE,0)) PAGE_AVG_SIZE,
     SUM(NVL(FST_PAGE_ACK_NUM,0)) FST_PAGE_ACK_NUM,
     SUM(NVL(DATATRANS_DW_DURATION,0)) DATATRANS_DW_DURATION,
     SUM(NVL(PAGE_SR_DELAY_MSEL,0)) PAGE_SR_DELAY_MSEL 
    FROM
     PS.SDR_WEB_BSCRNC_1DAY SDR
     INNER JOIN (SELECT
         BSCRNC_ID,
         BSCRNC_NAME,
         ACCESS_TYPE,
         ACCESS_TYPE_ID 
        FROM
         nethouse.DIM_LOC_BSCRNC 
        GROUP BY
         BSCRNC_ID,
         BSCRNC_NAME,
         ACCESS_TYPE,
         ACCESS_TYPE_ID) DIM 
     ON SDR.BSCRNC_ID = DIM.BSCRNC_ID 
     AND DIM.ACCESS_TYPE_ID IN (0,1,2) 
     INNER JOIN nethouse.DIM_RAT_MAPPING RAT 
     ON (RAT.RAT = SDR.RAT)
    WHERE
     ( (STARTTIME >= 1461340800 
     AND STARTTIME < 1461427200) ) 
     AND RAT.ACCESS_TYPE_ID IN (0,1,2) 
     and SDR.BSCRNC_ID is not null
    GROUP BY
     STTIME ) ) A;
   ```
   执行计划如[图2]所示。
   图2增加JOIN列非空条件（二）   
   ![](https://support.huaweicloud.com/distributed-devg-v2-gaussdb/figure/zh-cn_image_0000002220984825.jpg "点击放大")