具有多個AND和OR的SQL CASE WHEN

Question

您能告訴我下面的SQL代碼是否有意義。 我在CASE WHEN使用多個ANDs和OR 。 謝謝你的幫助！

SELECT id, period,
 CASE WHEN state = 'group8' AND mathscore = 0 AND manager = '' OR manager ISNULL 
 THEN 'Tom' ELSE manager END AS mgr, 

 CASE WHEN state = 'group8' AND mathscore = 0 AND associate = '' OR associate 
 ISNULL THEN 'Dick' ELSE associate END AS asso,

 CASE WHEN state = 'group8' AND mathscore = 0 AND analyst = '' OR analyst ISNULL 
 THEN 'Harry' ELSE analyst END AS a

 FROM class.sections 

Answer 1

使用AND和OR時，應將其括在括號中，以免產生不良結果。 即：

CASE WHEN (state = 'group8' AND mathscore = 0)
AND (manager = '' OR manager ISNULL)
THEN 'Tom' ELSE manager END AS mgr

與以下內容不同：

CASE WHEN (state = 'group8' AND mathscore = 0 AND manager = '')
OR manager ISNULL 
THEN 'Tom' ELSE manager END AS mgr

Answer 2

如果沒有可使用的示例數據，我會押注您正在尋找類似的東西，您的空格和NULL與括號一起分組。

另外，我將您的ISNULL （在某些方言中為函數）更改為IS NULL （在SQL Server中為狀態，無論如何）。

SELECT
  id
 ,period
 ,CASE
    WHEN state = 'group8'
         AND mathscore = 0
         AND (manager = ''
             OR manager IS NULL) THEN 'Tom'
    ELSE manager
  END AS mgr
 ,CASE
    WHEN state = 'group8'
         AND mathscore = 0
         AND (associate = ''
             OR associate IS NULL) THEN 'Dick'
    ELSE associate
  END AS asso
 ,CASE
    WHEN state = 'group8'
         AND mathscore = 0
         AND (analyst = ''
             OR analyst IS NULL) THEN 'Harry'
    ELSE analyst
  END AS a
FROM
  class.sections;