SQL中的子查詢中的子查詢 - DB2

Question

我在嘗試根據查詢返回的結果之一動態地在第一個篩選器中顯示子查詢時遇到問題。有人可以告訴我我做錯了什麼。在第一個子查詢中工作。

 (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 

以上是我試圖從查詢與CTXTKEY或CTXT.N_COD_METER_CNTX_KEY替換123456的子查詢。以下是完整的代碼。請注意，比在「MAX_NUM_CONS_DAYS」之前的子查詢中有效。但是，這只是一個子查詢。

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 )))) 
) 

錯誤，我得到的是：

錯誤代碼：-204，SQL狀態：42704

Answer 1

不能從外部選擇引用列的子查詢，不超過無論如何1層深。如果我正確理解你在做什麼，你可能需要在外部選擇中加入DWH.MQT_SUMMARY_WATER_READINGS和DWH.DWH_WMETER_CONTEXT。

Answer 2

我會說這裏的一個好的選擇是使用CTE或公用表表達式。你可以做類似下面的東西：

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; 

雖然這不是針對你的例子，但它表明，CTE的「內存」中產生一種暫時的，你可以在隨後的查詢訪問表。這應該允許您發出內部兩個子查詢作爲CTE，然後在「SELECT MAX（MAX_DATE - MIN_DATE）AS NUM_CONS_DAYS」查詢中使用CTE。