SQL：从 SQL CASE 语句返回表达式

Question

在此先感谢，我使用的是 oracle 10g。在 SQL case 语句中，我们传递值并根据值检查大小写并返回字符串。但我不想返回字符串，而是返回一个表达式。这是否可以使用 oracle SQL 查询 CASE 语句返回表达式？我执行以下操作，oracle 生成错误ORA-00905:Missing Keyword

SELECT ECL_CONTROL,
  CASE 
    WHEN ECL_CONTROL = 'N' THEN ('##0') = ('##0')
    WHEN ECL_CONTROL = 'Y' THEN (NVL(IL.ECL, 'X') = NVL(IM.ECL, 'X'))
  END
FROM ITEM_CONTROL WHERE ITEM_NO =  '2N2907A' 

但以下运行成功：

SELECT ECL_CONTROL,
  CASE 
    WHEN ECL_CONTROL = 'N' THEN 'test'
    WHEN ECL_CONTROL = 'Y' THEN 'demo'
  END
FROM ITEM_CONTROL WHERE ITEM_NO =  '2N2907A'

我想使用这个查询作为内部查询和外部查询的返回和表达式。我的查询如下：

SELECT  LSM.ACTIVE_FLAG, LSM.ITEM_NO, IL.ECL, LSM.SERIAL_NO, IL.WAREHOUSE, IL.BIN, LSM.TOOL_STATUS_CODE,
LLG.NEXT_CAL_DATE, IM.PRODUCT_GROUP
FROM LS_SERIAL_MASTER LSM, LS_LIFE_LOG LLG, ITEM_LOCATION IL, ITEM_MASTER IM
WHERE   IL.PLANT = IM.PLANT AND IL.ITEM_NO = IM.ITEM_NO 
AND IM.PLANT = LSM.PLANT AND IM.ITEM_NO = LSM.ITEM_NO AND NVL(IM.PRODUCT_GROUP, 'X') =    NVL('PUMP', 'X')
AND LSM.PLANT = LLG.PLANT AND LSM.ITEM_NO = LLG.ITEM_NO AND LSM.SERIAL_NO = LLG.SERIAL_NO
AND LSM.LIFE_TRANS_ID = LLG.TRANS_ID AND LLG.SERIAL_NO = IL.SERIAL_NO
AND (SELECT ECL_CONTROL,
  CASE ECL_CONTROL
    WHEN ECL_CONTROL = 'N' THEN ('##0' = '##0')
    WHEN ECL_CONTROL = 'Y' THEN (NVL(IL.ECL, 'X') = NVL(IM.ECL, 'X'))
  END AS ECL_CONTROL_TXT
  FROM ITEM_CONTROL WHERE ITEM_NO =  '2N2907A')
AND LLG.MAINT_LMT_ID IN('T', 'U')
AND LLG.NEXT_CAL_DATE BETWEEN TO_DATE('02/1/2014', 'MM/DD/YYYY') AND TO_DATE('02/11/2014', 'MM/DD/YYYY').

我的实际任务是从内部查询返回一个表达式并在外部查询中使用。

Answer 1

不，您展示的内容是不可能的。在select 中有一个表达式真的没有意义。你可以have an expression evaluated instead of using a fixed string:

SELECT ECL_CONTROL,
  CASE 
    WHEN ECL_CONTROL = 'N' THEN '##0'
    WHEN ECL_CONTROL = 'Y' THEN NVL(IL.ECL, 'X')
  END
FROM ITEM_CONTROL WHERE ITEM_NO =  '2N2907A' 

但是你不能返回实际的表达式。在您显示的代码中，第一个表达式总是会评估为 true 无论如何（并且布尔值也不存在于普通 SQL 中），所以我认为这可能是您的实际意图，您对如何分配感到困惑表达式值。你还没有显示IL 和IM 的来源，所以很难说清楚你想要什么。

您可以在where 子句中直接使用case：

SELECT ...
FROM IM, IL, ITEM_CONTROL -- joined in some way
WHERE CASE 
    WHEN ECL_CONTROL = 'N' THEN '##0'
    WHEN ECL_CONTROL = 'Y' THEN NVL(IL.ECL, 'X')
  END = CASE 
    WHEN ECL_CONTROL = 'N' THEN '##0'
    WHEN ECL_CONTROL = 'Y' THEN NVL(IM.ECL, 'X')
  END

虽然这可能更清楚：

WHERE ECL_CONTROL = 'N' OR NVL(IL.ECL, 'X') = NVL(IM.ECL, 'X')

从您添加的更大查询中：

SELECT LSM.ACTIVE_FLAG, LSM.ITEM_NO, IL.ECL, LSM.SERIAL_NO, IL.WAREHOUSE,
  IL.BIN, LSM.TOOL_STATUS_CODE, LLG.NEXT_CAL_DATE, IM.PRODUCT_GROUP
FROM LS_SERIAL_MASTER LSM, LS_LIFE_LOG LLG, ITEM_LOCATION IL, ITEM_MASTER IM
WHERE IL.PLANT = IM.PLANT AND IL.ITEM_NO = IM.ITEM_NO 
AND IM.PLANT = LSM.PLANT AND IM.ITEM_NO = LSM.ITEM_NO
AND NVL(IM.PRODUCT_GROUP, 'X') = NVL('PUMP', 'X')
AND LSM.PLANT = LLG.PLANT AND LSM.ITEM_NO = LLG.ITEM_NO
AND LSM.SERIAL_NO = LLG.SERIAL_NO
AND LSM.LIFE_TRANS_ID = LLG.TRANS_ID AND LLG.SERIAL_NO = IL.SERIAL_NO
AND LLG.MAINT_LMT_ID IN('T', 'U')
AND LLG.NEXT_CAL_DATE BETWEEN TO_DATE('02/1/2014', 'MM/DD/YYYY')
  AND TO_DATE('02/11/2014', 'MM/DD/YYYY')
AND ((SELECT ECL_CONTROL FROM ITEM_CONTROL WHERE ITEM_NO = '2N2907A') = 'N'
  OR NVL(IL.ECL, 'X') = NVL(IM.ECL, 'X'))

...虽然由于子查询正在寻找单行 - 具有固定的item_no 与您在其他表中引用的具有相同名称的其他列相关 - 您可以只在主查询中包含该表.

无论如何。顺便说一句，使用显式连接会更清楚；而是超出了问题的范围，但接受您的评论，即item_no 实际上是相关的，例如：

SELECT LSM.ACTIVE_FLAG, LSM.ITEM_NO, IL.ECL, LSM.SERIAL_NO, IL.WAREHOUSE,
  IL.BIN, LSM.TOOL_STATUS_CODE, LLG.NEXT_CAL_DATE, IM.PRODUCT_GROUP
FROM LS_LIFE_LOG LLG
JOIN LS_SERIAL_MASTER LSM ON LSM.PLANT = LLG.PLANT
  AND LSM.ITEM_NO = LLG.ITEM_NO
  AND LSM.SERIAL_NO = LLG.SERIAL_NO
  AND LSM.LIFE_TRANS_ID = LLG.TRANS_ID
JOIN ITEM_CONTROL IC ON IC.ITEM_NO = LSM.ITEM_NO
JOIN ITEM_MASTER IM ON IM.PLANT = LSM.PLANT
  AND IM.ITEM_NO = IC.ITEM_NO
JOIN ITEM_LOCATION IL ON IL.PLANT = IM.PLANT
  AND IL.ITEM_NO = IM.ITEM_NO
  AND IL.SERIAL_NO = LLG.SERIAL_NO
  AND (IC.ECL_CONTROL = 'N' OR NVL(IL.ECL, 'X') = NVL(IM.ECL, 'X'))
WHERE LLG.MAINT_LMT_ID IN ('T', 'U')
AND LLG.NEXT_CAL_DATE BETWEEN TO_DATE('02/1/2014', 'MM/DD/YYYY')
  AND TO_DATE('02/11/2014', 'MM/DD/YYYY')
AND NVL(IM.PRODUCT_GROUP, 'X') = NVL('PUMP', 'X')

NVL('PUMP', 'X') 虽然没有意义 - NVL() 在固定值附近毫无意义。也许你的意思不是AND NVL(IM.PRODUCT_GROUP, 'X') = NVL('PUMP', 'X')，而是AND (IM.PRODUCT_GROUP IS NULL OR IM.PRODUCT_GROUP = 'PUMP')？