如何在同一個表的同一列上使用不同的where子句連接SQL語句

Question

我在sqlite中有2個語句

第一份聲明：

Select SUM(GrossQty) As GQTY, SUM(NetQty) As NQTY
  From NSales 
  Where IMonth=5 And IYear=2012 And IDay>15

結果：

\n GQty NQty\n  30 25\n

第二個聲明

Select SUM(GrossQty) As GQTY, SUM(NetQty) As NQTY
  From NSales 
  Where IMonth=6 And IYear=2012 And IDay<10

第二個結果：

\n GQty NQty\n  20 15\n

我如何組合這些語句，以便將這些結果添加到一起？

期望的結果：

\n GQty NQty\n  50 40\n

Answer 1

你可以做：

SELECT 
    SUM(a.GQTY) AS GrossQty, 
    SUM(a.NQTY) AS NQTY
FROM
(
    SELECT SUM(GrossQty) AS GQTY, SUM(NetQty) AS NQTY 
    FROM   NSales 
    WHERE  IMonth = 5 AND IYear = 2012 AND IDay > 15

    UNION ALL

    SELECT SUM(GrossQty), SUM(NetQty)
    FROM   NSales
    WHERE  IMonth = 6 AND IYear = 2012 AND IDay < 10
) a

或者：

SELECT 
    a.GQTY + b.GQTY AS GQTY,
    a.NQTY + b.NQTY AS NQTY
FROM
(
    SELECT SUM(GrossQty) AS GQTY, SUM(NetQty) AS NQTY 
    FROM   NSales 
    WHERE  IMonth = 5 AND IYear = 2012 AND IDay > 15
) a
CROSS JOIN
(
    SELECT SUM(GrossQty) AS GQTY, SUM(NetQty) NQTY
    FROM   NSales
    WHERE  IMonth = 6 AND IYear = 2012 AND IDay < 10
) b

或者您可以使用CASE表達式並避免必須發出兩個單獨的子選擇（更難閱讀）：

SELECT 
    SUM(
        CASE WHEN (IMonth = 5 AND IYear = 2012 AND IDay > 15) OR
                  (IMonth = 6 AND IYear = 2012 AND IDay < 10) THEN
                  GrossQty
             ELSE 0
        END) AS GQTY, 
    SUM(
        CASE WHEN (IMonth = 5 AND IYear = 2012 AND IDay > 15) OR
                  (IMonth = 6 AND IYear = 2012 AND IDay < 10) THEN
                  NetQty
             ELSE 0
        END) AS NQTY
FROM NSales