“where”子句中的SQL Switch / Case
-
03-07-2019 - |
题
我试着四处寻找,但我找不到任何可以帮助我的东西。
我正在尝试在SQL中执行此操作:
declare @locationType varchar(50);
declare @locationID int;
SELECT column1, column2
FROM viewWhatever
WHERE
CASE @locationType
WHEN 'location' THEN account_location = @locationID
WHEN 'area' THEN xxx_location_area = @locationID
WHEN 'division' THEN xxx_location_division = @locationID
我知道我不应该在每一行的末尾放置'= @locationID',但我无法使语法接近正确。 SQL在第一个WHEN行上一直抱怨我的'='...
我该怎么做?
解决方案
declare @locationType varchar(50);
declare @locationID int;
SELECT column1, column2
FROM viewWhatever
WHERE
@locationID =
CASE @locationType
WHEN 'location' THEN account_location
WHEN 'area' THEN xxx_location_area
WHEN 'division' THEN xxx_location_division
END
其他提示
没有案例陈述......
SELECT column1, column2
FROM viewWhatever
WHERE
(@locationType = 'location' AND account_location = @locationID)
OR
(@locationType = 'area' AND xxx_location_area = @locationID)
OR
(@locationType = 'division' AND xxx_location_division = @locationID)
你走了。
SELECT
column1,
column2
FROM
viewWhatever
WHERE
CASE
WHEN @locationType = 'location' AND account_location = @locationID THEN 1
WHEN @locationType = 'area' AND xxx_location_area = @locationID THEN 1
WHEN @locationType = 'division' AND xxx_location_division = @locationID THEN 1
ELSE 0
END = 1
我会说这是一个有缺陷的表结构的指标。也许不同的位置类型应该在不同的表中分开,这使您可以进行更丰富的查询,并避免使用多余的列。
如果您无法更改结构,可能会运行以下内容:
SELECT
*
FROM
Test
WHERE
Account_Location = (
CASE LocationType
WHEN 'location' THEN @locationID
ELSE Account_Location
END
)
AND
Account_Location_Area = (
CASE LocationType
WHEN 'area' THEN @locationID
ELSE Account_Location_Area
END
)
依此类推......我们无法动态更改查询的结构,但我们可以通过使谓词相等来覆盖它。
编辑:上述建议当然要好得多,只要忽略我的。这个问题是当SQL引擎去评估表达式时,它会检查FROM部分以获取正确的表,然后检查WHERE部分以提供一些基本条件,因此它无法正确评估动态条件要检查的列。
当您检查谓词中的WHERE条件时,可以使用WHERE子句,例如
WHERE account_location = CASE @locationType
WHEN 'business' THEN 45
WHEN 'area' THEN 52
END
因此,在您的特定情况下,您将需要将查询放入存储过程或创建三个单独的查询。
OR运算符可以在where where condition
时替代caseALTER PROCEDURE [dbo].[RPT_340bClinicDrugInventorySummary]
-- Add the parameters for the stored procedure here
@ClinicId BIGINT = 0,
@selecttype int,
@selectedValue varchar (50)
AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;
SELECT
drugstock_drugname.n_cur_bal,drugname.cdrugname,clinic.cclinicname
FROM drugstock_drugname
INNER JOIN drugname ON drugstock_drugname.drugnameid_FK = drugname.drugnameid_PK
INNER JOIN drugstock_drugndc ON drugname.drugnameid_PK = drugstock_drugndc.drugnameid_FK
INNER JOIN drugndc ON drugstock_drugndc.drugndcid_FK = drugndc.drugid_PK
LEFT JOIN clinic ON drugstock_drugname.clinicid_FK = clinic.clinicid_PK
WHERE (@ClinicId = 0 AND 1 = 1)
OR (@ClinicId != 0 AND drugstock_drugname.clinicid_FK = @ClinicId)
-- Alternative Case When You can use OR
AND ((@selecttype = 1 AND 1 = 1)
OR (@selecttype = 2 AND drugname.drugnameid_PK = @selectedValue)
OR (@selecttype = 3 AND drugndc.drugid_PK = @selectedValue)
OR (@selecttype = 4 AND drugname.cdrugclass = 'C2')
OR (@selecttype = 5 AND LEFT(drugname.cdrugclass, 1) = 'C'))
ORDER BY clinic.cclinicname, drugname.cdrugname
END
请尝试此查询。 回答上面的帖子:
select @msgID, account_id
from viewMailAccountsHeirachy
where
CASE @smartLocationType
WHEN 'store' THEN account_location
WHEN 'area' THEN xxx_location_area
WHEN 'division' THEN xxx_location_division
WHEN 'company' THEN xxx_location_company
END = @smartLocation
试试这个:
WHERE (
@smartLocationType IS NULL
OR account_location = (
CASE
WHEN @smartLocationType IS NOT NULL
THEN @smartLocationType
ELSE account_location
END
)
)
Case Statement in SQL Server Example
Syntax
CASE [ expression ]
WHEN condition_1 THEN result_1
WHEN condition_2 THEN result_2
...
WHEN condition_n THEN result_n
ELSE result
END
Example
SELECT contact_id,
CASE website_id
WHEN 1 THEN 'TechOnTheNet.com'
WHEN 2 THEN 'CheckYourMath.com'
ELSE 'BigActivities.com'
END
FROM contacts;
OR
SELECT contact_id,
CASE
WHEN website_id = 1 THEN 'TechOnTheNet.com'
WHEN website_id = 2 THEN 'CheckYourMath.com'
ELSE 'BigActivities.com'
END
FROM contacts;
尝试此查询。它很容易理解:
CREATE TABLE PersonsDetail(FirstName nvarchar(20), LastName nvarchar(20), GenderID int);
GO
INSERT INTO PersonsDetail VALUES(N'Gourav', N'Bhatia', 2),
(N'Ramesh', N'Kumar', 1),
(N'Ram', N'Lal', 2),
(N'Sunil', N'Kumar', 3),
(N'Sunny', N'Sehgal', 1),
(N'Malkeet', N'Shaoul', 3),
(N'Jassy', N'Sohal', 2);
GO
SELECT FirstName, LastName, Gender =
CASE GenderID
WHEN 1 THEN 'Male'
WHEN 2 THEN 'Female'
ELSE 'Unknown'
END
FROM PersonsDetail
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