使用來自不同行的值的 CASE 表達式

Question

我有下表

WITH TMP AS (
SELECT 'XX' AS AGG, 50 AS VALUE, 0 AS MONTH
UNION ALL
SELECT 'XX' AS AGG, 150 AS VALUE, 1 AS MONTH
UNION ALL
SELECT 'XX' AS AGG, 300 AS VALUE, 2 AS MONTH
UNION ALL
SELECT 'YY' AS AGG, 25 AS VALUE, 0 AS MONTH
UNION ALL
SELECT 'YY' AS AGG, 50 AS VALUE, 1 AS MONTH
UNION ALL
SELECT 'YY' AS AGG, 75 AS VALUE, 2 AS MONTH
UNION ALL
SELECT 'ZZ' AS AGG, 500 AS VALUE, 0 AS MONTH
UNION ALL
SELECT 'ZZ' AS AGG, 600 AS VALUE, 1 AS MONTH
UNION ALL
SELECT 'ZZ' AS AGG, 700 AS VALUE, 2 AS MONTH
)
-- CASE WHEN VALUE OF 'XX' > 0 THEN VALUE OF 'ZZ' ELSE 0 END
SELECT 
*
FROM TMP
WHERE 1 = 1

我需要始終考慮月份對其應用以下業務邏輯。

'XX' 的值 > 0 的情況，然后 'ZZ' 的值 ELSE 0 END

這個邏輯應該映射到一個新表中。 結果應如下表所示。
我想避免加入同一張表。 這是否可能使用窗口函數或類似的東西？ 這個想法是在同一個 sql 語句中構建幾個 case when 語句作為上面的一個。

IE1	月
500	00
600	01
700	02

Answer 1

透視（有條件地聚合）您的數據，然后根據您的表達式返回您需要的值：

WITH TMP AS
    (SELECT 'XX' AS AGG,
            50 AS VALUE,
            0 AS MONTH
     UNION ALL
     SELECT 'XX' AS AGG,
            150 AS VALUE,
            1 AS MONTH
     UNION ALL
     SELECT 'XX' AS AGG,
            300 AS VALUE,
            2 AS MONTH
     UNION ALL
     SELECT 'YY' AS AGG,
            25 AS VALUE,
            0 AS MONTH
     UNION ALL
     SELECT 'YY' AS AGG,
            50 AS VALUE,
            1 AS MONTH
     UNION ALL
     SELECT 'YY' AS AGG,
            75 AS VALUE,
            2 AS MONTH
     UNION ALL
     SELECT 'ZZ' AS AGG,
            500 AS VALUE,
            0 AS MONTH
     UNION ALL
     SELECT 'ZZ' AS AGG,
            600 AS VALUE,
            1 AS MONTH
     UNION ALL
     SELECT 'ZZ' AS AGG,
            700 AS VALUE,
            2 AS MONTH),
--Solution
/*WITH */Pvt AS(
    SELECT Month,
           MAX(CASE Agg WHEN 'XX' THEN VALUE END) AS XX,
           --MAX(CASE Agg WHEN 'YY' THEN VALUE END) AS YY,--Not needed hence commented out
           MAX(CASE Agg WHEN 'ZZ' THEN VALUE END) AS ZZ
    FROM TMP
    GROUP BY MONTH)
SELECT CASE WHEN XX > 0 THEN ZZ ELSE 0 END AS IE1,
       MONTH
FROM Pvt;