加倍在哪裏條件

Question

是否有可能做這樣的事情發生在這裏在where語句@Age帕拉姆？這樣做的

@AGE Varchar(8) 

SELECT NAME FROM TABLE WHERE 
(
If @AGE='man' 
    then (AGE = 'man' or AGE = 'boy') 
    else (AGE = 'man') 
) 
AND City IS NULL 

Answer 1

是的，是這樣的：

SELECT NAME FROM TABLE WHERE 
((@AGE='man' 
    AND (AGE = 'man' or AGE = 'boy')) 
OR 
(@AGE <> 'man' 
    AND (AGE = 'man'))) 
AND City IS NULL 

注意病情@AGE <> 'man'可能需要根據@AGE變量是否可以爲null，進行調整。

我回答了一個非常類似的問題here。

這是WHERE子句中非常常見的技術。如果你想 在WHERE子句中應用一些「IF」邏輯，你需要做的就是將帶有布爾AND的額外條件添加到 需要應用的部分。

Answer 2

一個方法是用EXEC和If's建立字符串命令。

是這樣的：

declare @t nvarchar(max) 
@AGE Varchar(8) 
set @t=' SELECT NAME FROM TABLE WHERE ' 


If @AGE='man' set @t=@t+'(AGE = ''man'' or AGE = ''boy'')' 
    else set @t=@t+'(AGE = 'man')' 

set @t=@t+' AND City IS NULL' 

Answer 3

或者你可以使用decode functions

Answer 4

在合取範式（「等一系列與運算的」，較少地依賴於parans）：

SELECT * 
    FROM TABLE 
WHERE (@AGE <> 'man' OR (AGE IN ('man', 'boy'))) 
     AND (@AGE = 'man' OR AGE = 'man') 
     AND CITY IS NULL; 

這裏的想法是使用蘊含重寫規則：

(IF x THEN y) is equivalent to (NOT (x) OR y) 

---

這裏的一些測試代碼：

WITH T 
    AS 
    (
     SELECT * 
     FROM (
       VALUES (1, 'man', NULL), 
        (2, 'boy', NULL), 
        (3, 'girl', NULL) 
      ) AS T (NAME, AGE, CITY) 
    ), 
    Params 
    AS 
    (
     SELECT * 
     FROM (
       VALUES ('man'), 
        ('boy'), 
        ('girl') 
      ) AS T (p_AGE) 
    ), 
    Results 
    AS 
    (
     SELECT Params.*, T.*, 
      CASE WHEN  ((p_AGE <> 'man' OR (AGE IN ('man', 'boy'))) AND (p_AGE = 'man' OR AGE = 'man')) THEN 'TRUE' 
        WHEN NOT ((p_AGE <> 'man' OR (AGE IN ('man', 'boy'))) AND (p_AGE = 'man' OR AGE = 'man')) THEN 'FALSE' 
        ELSE 'UNKNOWN' 
      END AS result_onedaywhen, 
      CASE WHEN  (AGE='man' OR (p_AGE='MAN' and AGE='boy')) THEN 'TRUE' 
        WHEN NOT (AGE='man' OR (p_AGE='MAN' and AGE='boy')) THEN 'FALSE' 
        ELSE 'UNKNOWN' 
      END AS result_Damien_The_Unbeliever 
     FROM T, Params 
    ) 
SELECT * 
    FROM Results;