where子句中case子句的用法

Question

我需要根据下拉值

为存储过程添加过滤器

可用值为0,1,2,3,4,5。 @TescilDurum是我的参数。

0 = ALL
1 = TescilDurumId IN 4 OR 5
2 = t.ID IS NULL
3 = dncts.RegistrationCode IS NULL
4 = hsm.ID IS NULL AND dncts.RegistrationCode IS NULL IS NOT NULL
5 = hsm.ENSMRN IS NULL

到目前为止，我在互联网上的类似问题答案中尝试了这一点，但我不确定这是否正确。我不确定这＆＃34;反向逻辑＆＃34;这是正确的方法。并且它之后的顺序也给出了错误......

AND 1 =
    CASE WHEN @TescilDurum = 1 AND t.TescilDurumId NOT IN (4,5) THEN 0 
    ELSE CASE WHEN @TescilDurum = 2 AND t.Id IS NOT NULL THEN 0
    ELSE CASE WHEN @TescilDurum = 3 AND hsm.EnsMRN IS NOT NULL THEN 0
    ELSE CASE WHEN @TescilDurum = 4 AND hsm.Id IS NOT NULL AND dncts.RegistrationCode IS NULL THEN 0
    ELSE CASE WHEN @TescilDurum = 5 AND hsm.EnsMRN IS NOT NULL THEN 0
    ELSE 1 END

Answer 1

您可以简化它：

WHERE 
  (CASE 
       WHEN @TescilDurum = 0 THEN 1
       WHEN @TescilDurum = 1 AND TescilDurumId IN (4,5) THEN 1
       WHEN @TescilDurum = 2 AND t.ID IS NULL THEN 1
       WHEN @TescilDurum = 3 AND dncts.RegistrationCode IS NULL THEN 1
       WHEN @TescilDurum = 4 AND hsm.ID IS NULL AND dncts.RegistrationCode IS NOT NULL THEN 1
       WHEN @TescilDurum = 5 AND hsm.ENSMRN IS NULL THEN 1
       ELSE NULL    -- this is default and can be skipped if needed
  END) = 1

修改

对于任何担心上述查询始终为1 = 1的人：

CASE具有默认的ELSE NULL子句，因此如果没有匹配，则整个语句将返回NULL和NULL = 1 => NULL。

DECLARE @v INT = 4;

SELECT 1
WHERE(CASE WHEN @v = 1 THEN 1
           WHEN @v = 2 THEN 1
           WHEN @v = 3 THEN 1
           ELSE NULL    -- this is default and can be skipped if needed
      END) = 1
 -- empty resultset

和

CREATE TABLE #tab(ID INT, col VARCHAR(100));

INSERT INTO #tab
VALUES (1, 'aa'), (2, 'bbb'), (3, NULL), (4, 'aa');

-- DROP DOWN MENU
-- 1 all records
-- 2 only those which ID is in (2,3)
-- 3 only those which has col = 'aa'
-- 4 only those which has NULL value in col

DECLARE @variable INT = 3;

SELECT *
FROM #tab
WHERE 
(
  CASE WHEN @variable = 1 THEN 1
       WHEN @variable = 2 AND ID IN (2,3) THEN 1
       WHEN @variable = 3 AND col = 'aa'  THEN 1
       WHEN @variable = 4 AND col IS NULL THEN 1
       ELSE NULL    -- this is default and can be skipped if needed
 END
) = 1

请注意，AND存在复合条件，因此将返回正确的行。

的 LiveDemo