Sql 寻找建议：如果我能在我的查询中避免所有的联合？

我有一个名为

SOURCE\u table

的表，其中有3列特定于一天，表示周日的SUN\u W、SUN\u WA和SUN\u WB，周一重复为MON\u W、MON\u WA和MON\u WB等，总共有3 x 7=21列

有没有更好的方法重写下面的查询并避免使用UNIONALL

      SELECT * FROM
      (SELECT 
      /*+ parallel(scr,10)
          parallel(el,10)  */ scr.rowid  AS "row_id", scr.*
      FROM SOURCE_TABLE scr
      LEFT OUTER JOIN CITY el ON (el.CITY_NAME  = scr.SUN_W)
      WHERE (el.ROWID IS NOT NULL AND scr.SUN_W IS NOT NULL
      AND GREATEST(scr.SUN_WA, scr.SUN_WB ) IS NULL)
      OR (el.ROWID IS NULL AND scr.SUN_W IS NOT NULL)

      UNION ALL

      SELECT 
      /*+ parallel(scr,10)
          parallel(el,10)  */ scr.rowid  AS "row_id", scr.*
      FROM SOURCE_TABLE scr
      LEFT OUTER JOIN CITY el ON (el.CITY_NAME  = scr.MON_W)
      WHERE (el.ROWID IS NOT NULL AND scr.MON_W IS NOT NULL
      AND GREATEST(scr.MON_WA, scr.MON_WB ) IS NULL)
      OR (el.ROWID IS NULL AND scr.MON_W IS NOT NULL)


      UNION ALL

      SELECT 
      /*+ parallel(scr,10)
          parallel(el,10)  */ scr.rowid  AS "row_id", scr.*
      FROM SOURCE_TABLE scr
      LEFT OUTER JOIN CITY el ON (el.CITY_NAME  = scr.TUE_W)
      WHERE (el.ROWID IS NOT NULL AND scr.TUE_W IS NOT NULL
      AND GREATEST(scr.TUE_WA, scr.TUE_WB ) IS NULL)
      OR (el.ROWID IS NULL AND scr.TUE_W IS NOT NULL)

      UNION ALL 

      ...

      )

---

一两个可能有帮助，也可能没有帮助的建议。看一看、测试、决定

这：

我觉得很可疑。为什么要测试

ROWID是否为NULL

？它不能为空，对吗？因此，它可以缩短为

WHERE scr.sun_w is not null 
  AND greatest(scr.sun_wa, scr.sun_wb) is null

此外，如果一个（或两个）参数是

NULL

，则

magest

将是

NULL

，因此它将是

WHERE scr.sun_w is not null
  AND (   scr.sun_wa is null 
       OR scr.sun_wb is null
      )

我不知道哪一个会表现得更好。如果

grest

工作正常，就不要管它，尽管你要找的东西并不那么明显

---

我不确定这是否等同于您的查询（无法测试，没有您的数据），但是-看看它是否有意义（包含截至周二的列）：

---

查询无效<代码>cns未定义。@GordonLinoff更新了问题，这是一个打字错误！！谢谢@Littlefoot这个建议很有帮助！

WHERE scr.sun_w is not null
  AND (   scr.sun_wa is null 
       OR scr.sun_wb is null
      )

select *
from source_table scr left outer join city el 
  on el.city_name in (scr.sun_w, scr.mon_w, scr.tue_w)
where 
  (    scr.sun_w is not null
   and greatest(scr.sun_wa, scr.sun_wb) is null
  )
  or
  (    scr.mon_w is not null
   and greatest(scr.mon_wa, scr.mon_wb) is null
  )
  or
  (    scr.tue_w is not null
   and greatest(scr.tue_wa, scr.tue_wb) is null
  );