这是一个非常复杂的话题,具有许多微妙的性能影响。你真的需要通过厄兰Sommarskog阅读这些优秀的文章:
Dynamic Search Conditions in T-SQL
The Curse and Blessings of Dynamic SQL
既然没有“一刀切”这种查询方法,也有细微的性能影响你该怎么办这个。如果您想超越只是让查询返回正确的答案,不管它有多慢,看看这篇文章:Dynamic Search Conditions in T-SQL by Erland Sommarskog。它涵盖了每种方法,并且非常详细地给出了每种方法的PRO和Cons。
如果您可以确定搜索列的最小和最大可能范围,并且搜索列不是NULL,那么您可以比(@Search IS NULL或Col = @ Search),see this area of the above linked article做得更好。不过,你应该阅读整篇文章,有很多变化取决于你的情况,你真的需要学习多种方法以及何时使用它们。
如果您想在单个字符串参数中搜索多个术语,则需要拆分该字符串。
您需要创建一个拆分功能。这是一个分裂的功能如何使用:
SELECT
*
FROM YourTable y
INNER JOIN dbo.yourSplitFunction(@Parameter) s ON y.ID=s.Value
I prefer the number table approach to split a string in TSQL但也有许多方法来拆分在SQL Server中的字符串,见前面的链接,这说明各的优点和缺点。
对于数字表的方法来工作,你需要做的这一次表的设置,这将创建一个包含从1到10000行的表Numbers
:
SELECT TOP 10000 IDENTITY(int,1,1) AS Number
INTO Numbers
FROM sys.objects s1
CROSS JOIN sys.objects s2
ALTER TABLE Numbers ADD CONSTRAINT PK_Numbers PRIMARY KEY CLUSTERED (Number)
一旦Numbers表格设置,创建此分割功能:
CREATE FUNCTION [dbo].[FN_ListToTable]
(
@SplitOn char(1) --REQUIRED, the character to split the @List string on
,@List varchar(8000)--REQUIRED, the list to split apart
)
RETURNS TABLE
AS
RETURN
(
----------------
--SINGLE QUERY-- --this will not return empty rows
----------------
SELECT
ListValue
FROM (SELECT
LTRIM(RTRIM(SUBSTRING(List2, number+1, CHARINDEX(@SplitOn, List2, number+1)-number - 1))) AS ListValue
FROM (
SELECT @SplitOn + @List + @SplitOn AS List2
) AS dt
INNER JOIN Numbers n ON n.Number < LEN(dt.List2)
WHERE SUBSTRING(List2, number, 1) = @SplitOn
) dt2
WHERE ListValue IS NOT NULL AND ListValue!=''
);
GO
您现在可以轻松地拆分CSV字符串转换成表格,并加入就可以了:
select * from dbo.FN_ListToTable(',','1,2,3,,,4,5,6777,,,')
OUTPUT:
ListValue
-----------------------
1
2
3
4
5
6777
(6 row(s) affected)
您可以使用多个搜索标准字符串是这样的:
DECLARE @Persons table (FirstName varchar(50) , LastName varchar(50), EmailAddress varchar(200))
INSERT INTO @Persons VALUES ('aaa','bbb','[email protected]')
INSERT INTO @Persons VALUES ('xxx','yyy','[email protected]')
INSERT INTO @Persons VALUES ('aaa','yyy','[email protected]')
INSERT INTO @Persons VALUES ('111','222','[email protected]')
declare @searchTerm varchar(50)
set @searchTerm = 'aaa bbb'
--this should use an index on FirstName and LastName if they exist, no index usage on EmailAddress
select
p.* --<<"*" isn't good, only list the columns you need
FROM @Persons p
INNER JOIN dbo.FN_ListToTable(' ',@searchTerm) b on p.FirstName=b.Listvalue
UNION
select
p.* --<<"*" isn't good, only list the columns you need
FROM @Persons p
INNER JOIN dbo.FN_ListToTable(' ',@searchTerm) b on p.LastName=b.Listvalue
UNION
select
p.* --<<"*" isn't good, only list the columns you need
FROM @Persons p
INNER JOIN dbo.FN_ListToTable(' ',@searchTerm) b on p.EmailAddress like '%'+b.Listvalue+'%'
OUTPUT:
FirstName LastName EmailAddress
---------- ---------- -------------------------
aaa bbb [email protected]
aaa yyy [email protected]
xxx yyy [email protected]
(3 row(s) affected)
这种方法适用于任何数量的参数工作:
aaa
aaa
aaa bbb
aaa bbb
aaa bbb eee
aaa bbb eee ddd
aaa bbb eee