SQL / PLSQL Oracle查詢：WHERE語句中的CASE

Question

我正在嘗試查詢oracle數據庫，但無法完全使腳本正常工作。 該腳本是為了尋找員工提供一個start_date兩個日期之間。 不幸的是，並非所有員工在數據庫中都有start_date ，但是所有員工都具有create_date 。 我想做的是：

IF START_DATE IS NULL:
    (E.START_DATE >= TO_DATE('10/29/2014', 'MM/DD/YYYY') AND E.START_DATE <= TO_DATE('10/29/2016', 'MM/DD/YYYY')
ELSE: 
    (E.CREATE_DATE >= TO_DATE('10/29/2014', 'MM/DD/YYYY') AND E.CREATE_DATE <= TO_DATE('10/29/2016', 'MM/DD/YYYY')

這是我到目前為止的內容：

SELECT OC.DESCRIPTION "Description",
sum(S.AMOUNT) "SUM",
COUNT (DISTINCT(E.EMPLOYEE_NUM)) "Employee Nums"
FROM EMPLOYEES E
JOIN EMPLOYEE_SPENDING S ON S.EMPLOYEE_ID = E.EMPLOYEE_ID
WHERE E.EMPLOYEE_CATEGORY IN ('ACTIVE', 'INACTIVE')
AND ((E.START_DATE >= TO_DATE('10/29/2014', 'MM/DD/YYYY') AND E.START_DATE <= TO_DATE('10/29/2016', 'MM/DD/YYYY'))
OR (E.CREATE_DATE >= TO_DATE('10/29/2014', 'MM/DD/YYYY') AND E.CREATE_DATE <= TO_DATE('10/29/2016', 'MM/DD/YYYY')))
GROUP BY E.EMPLOYEE_CATEGORY;

我的案例陳述看起來像這樣：

SELECT OC.DESCRIPTION "Description",
sum(S.AMOUNT) "SUM",
COUNT (DISTINCT(E.EMPLOYEE_NUM)) "Employee Nums"
FROM EMPLOYEES E
JOIN EMPLOYEE_SPENDING S ON S.EMPLOYEE_ID = E.EMPLOYEE_ID
WHERE E.EMPLOYEE_CATEGORY IN ('ACTIVE', 'INACTIVE')
AND (CASE WHEN E.START_DATE IS NULL THEN (E.START_DATE >= TO_DATE('10/29/2014', 'MM/DD/YYYY') AND E.START_DATE <= TO_DATE('10/29/2016', 'MM/DD/YYYY'))
ELSE (E.CREATE_DATE >= TO_DATE('10/29/2014', 'MM/DD/YYYY') AND E.CREATE_DATE <= TO_DATE('10/29/2016', 'MM/DD/YYYY'))
END
GROUP BY E.EMPLOYEE_CATEGORY;

我對Oracle或PLSQL不太熟悉，因此，您能提供的任何幫助將不勝感激！

提前致謝！

Answer 1

我相信您的邏輯倒退。 這更有意義：

IF START_DATE IS NOT NULL:
    (E.START_DATE >= TO_DATE('10/29/2014', 'MM/DD/YYYY') AND E.START_DATE <= TO_DATE('10/29/2016', 'MM/DD/YYYY')
ELSE: 
    (E.CREATE_DATE >= TO_DATE('10/29/2014', 'MM/DD/YYYY') AND E.CREATE_DATE <= TO_DATE('10/29/2016', 'MM/DD/YYYY')

然后，您可以將其表示為：

where (e.start_date >= date '2014-10-29' and e.start_date <= date '2016-10-29') or
      (e.start_date is null and e.create_date >= date '2014-10-29' and e.start_date <= date '2016-10-29')

注意，我通過使用date關鍵字后跟一個ISO標准日期簡化了“日期常數”。

這可以進一步簡化為：

where coalesce(e.start_date, e.create_date) >= date '2014-10-29' and
      coalesce(e.start_date, e.create_date) <= date '2016-10-29'

通常，您要避免在where子句中使用case ，因為基本的布爾表達式通常很容易編寫和理解。 用case的時間是當您明確想要對條件進行排序時，尤其是當一個條件可能是昂貴的函數調用時。

Answer 2

像這樣使用nvl：

SELECT OC.DESCRIPTION "Description",
sum(S.AMOUNT) "SUM",
COUNT (DISTINCT(E.EMPLOYEE_NUM)) "Employee Nums"
FROM EMPLOYEES E
JOIN EMPLOYEE_SPENDING S ON S.EMPLOYEE_ID = E.EMPLOYEE_ID
WHERE E.EMPLOYEE_CATEGORY IN ('ACTIVE', 'INACTIVE')
AND ((nvl(E.START_DATE, e.create_date) >= TO_DATE('10/29/2014', 'MM/DD/YYYY') AND (nvl(E.START_DATE, e.create_date) <= TO_DATE('10/29/2016', 'MM/DD/YYYY'))
GROUP BY E.EMPLOYEE_CATEGORY;