SQL中的子查询中的子查询 - DB2

Question

我在尝试根据查询返回的结果之一动态地在第一个筛选器中显示子查询时遇到问题。有人可以告诉我我做错了什么。在第一个子查询中工作。

 (SELECT 
    MAX(MAX_DATE - MIN_DATE) AS NUM_CONS_DAYS 
    FROM 
    (
    SELECT 
     MIN(TMP.D_DAT_INDEX_DATE) AS MIN_DATE, 
     MAX(TMP.D_DAT_INDEX_DATE) AS MAX_DATE, 
     SUM(INDEX_COUNT)   AS SUM_INDEX 
    FROM 
     (
      SELECT 
       D_DAT_INDEX_DATE, 
       INDEX_COUNT, 
       D_DAT_INDEX_DATE - (DENSE_RANK() OVER(ORDER BY D_DAT_INDEX_DATE)) DAYS AS G 
      FROM 
       DWH.MQT_SUMMARY_WATER_READINGS 
      WHERE 
       N_COD_METER_CNTX_KEY = 79094 
     ) AS TMP 
    GROUP BY 
     TMP.G 
    ORDER BY 
     1 
)) AS MAX_NUM_CONS_DAYS 

以上是我试图从查询与CTXTKEY或CTXT.N_COD_METER_CNTX_KEY替换123456的子查询。以下是完整的代码。请注意，比在“MAX_NUM_CONS_DAYS”之前的子查询中有效。但是，这只是一个子查询。

SELECT 
    N_COD_WM_DWH_KEY, 
    V_COD_WM_SN_2, 
    N_COD_SP_ID, 
    CTXKEY, 
    V_COD_MIU_SN, 
    N_COD_POD, 
    MIU_CAT, 
    V_COD_SITR_ASSOCIATED, 
    WO_INST_DATE, 
    WO_MIU_CAT, 
    DAYSRECEIVED3, 
    MAX_NUM_CONS_DAYS, 
    (CASE WHEN (DAYSRECEIVED3 = 3) THEN 'Y' ELSE 'N' END) AS GREEN, 
    (CASE WHEN (DAYSRECEIVED3 < 3 AND DAYSRECEIVED3 > 0) THEN 'Y' ELSE 'N' END) AS BLUE, 
    (CASE WHEN (DAYSRECEIVED3 = 0 AND MAX_NUM_CONS_DAYS >= 5) THEN 'Y' ELSE 'N' END) AS ORANGE, 
    (CASE WHEN (DAYSRECEIVED3 = 0 AND MAX_NUM_CONS_DAYS BETWEEN 1 and 4) THEN 'Y' ELSE 'N' END) AS RED 

FROM 
(
SELECT 
    WMETER.N_COD_WM_DWH_KEY, 
    WMETER.V_COD_WM_SN_2, 
    WMETER.N_COD_SP_ID, 
    CTXT.N_COD_METER_CNTX_KEY AS CTXKEY, 
    CTXT.V_COD_MIU_SN, 
    CTXT.N_COD_POD, 
    MIU.N_COD_MIU_CATEGORY AS MIU_CAT, 
    CTXT.V_COD_SITR_ASSOCIATED, 
    T1.D_DAT_PLAN_INST AS WO_INST_DATE, 
    T1.N_COD_MIU_CATEGORY AS WO_MIU_CAT, 

    (SELECT COUNT(DISTINCT D_DAT_INDEX_DATE) FROM DWH.MQT_SUMMARY_WATER_READINGS WHERE (N_COD_METER_CNTX_KEY = CTXT.N_COD_METER_CNTX_KEY) AND D_DAT_INDEX_DATE BETWEEN ('2013-07-10') AND ('2013-07-12')) AS DAYSRECEIVED3, 

    (SELECT 
     MAX(MAX_DATE - MIN_DATE) AS NUM_CONS_DAYS 
     FROM 
     (
     SELECT 
      MIN(TMP.D_DAT_INDEX_DATE) AS MIN_DATE, 
      MAX(TMP.D_DAT_INDEX_DATE) AS MAX_DATE, 
      SUM(INDEX_COUNT)   AS SUM_INDEX 
     FROM 
      (
       SELECT 
        D_DAT_INDEX_DATE, 
        INDEX_COUNT, 
        D_DAT_INDEX_DATE - (DENSE_RANK() OVER(ORDER BY D_DAT_INDEX_DATE)) DAYS AS G 
       FROM 
        DWH.MQT_SUMMARY_WATER_READINGS 
       WHERE 
        N_COD_METER_CNTX_KEY = 79094 
      ) AS TMP 
     GROUP BY 
      TMP.G 
     ORDER BY 
      1 
    )) AS MAX_NUM_CONS_DAYS 



FROM DWH.DWH_WATER_METER AS WMETER 
LEFT JOIN DWH.DWH_WMETER_CONTEXT AS CTXT 
    ON WMETER.N_COD_WM_DWH_KEY = CTXT.N_COD_WM_DWH_KEY 
LEFT JOIN DWH.DWH_MIU AS MIU 
    ON CTXT.V_COD_MIU_SN = MIU.V_COD_MIU_SN 
LEFT JOIN 
    (SELECT V_COD_CORR_WAT_METER_SN, D_DAT_PLAN_INST, N_COD_MIU_CATEGORY 
     FROM DWH.DWH_ORDER_MANAGEMENT_FACT 
     JOIN DWH.DWH_MIU 
      ON DWH.DWH_ORDER_MANAGEMENT_FACT.V_COD_MIU_SN = DWH.DWH_MIU.V_COD_MIU_SN 
) AS T1 
    ON WMETER.V_COD_WM_SN_2 = T1.V_COD_CORR_WAT_METER_SN 
WHERE 
    (V_COD_SITR_ASSOCIATED = 'X') 
    AND ((MIU.N_COD_MIU_CATEGORY <> 4) OR ((MIU.N_COD_MIU_CATEGORY IS NULL) AND ((T1.N_COD_MIU_CATEGORY <> 4 ) OR (T1.N_COD_MIU_CATEGORY IS NULL )))) 
) 

错误，我得到的是：

错误代码：-204，SQL状态：42704

Answer 1

不能从外部选择引用列的子查询，不超过无论如何1层深。如果我正确理解你在做什么，你可能需要在外部选择中加入DWH.MQT_SUMMARY_WATER_READINGS和DWH.DWH_WMETER_CONTEXT。

Answer 2

我会说这里的一个好的选择是使用CTE或公用表表达式。你可以做类似下面的东西：

WITH CTE_X AS(
SELECT VAL_A 
     ,VAL_B 
    FROM TABLE_A) 
,CTE_Y AS(
SELECT VAL_C 
     ,VAL_B 
    FROM TABLE_B) 
SELECT VAL_A 
     ,VAL_B 
    FROM CTE_X X 
    JOIN CTE_Y Y 
     ON X.VAL_A = Y.VAL_C; 

虽然这不是针对你的例子，但它表明，CTE的“内存”中产生一种暂时的，你可以在随后的查询访问表。这应该允许您发出内部两个子查询作为CTE，然后在“SELECT MAX（MAX_DATE - MIN_DATE）AS NUM_CONS_DAYS”查询中使用CTE。