SQL实用札记【SQL Sever篇】

目录

1. 从表中去除重复行
2. 逗号分隔字符串转数据表行
3. 跨DB/Server执行SP[分布式事务]
4. 在OpenQuery中执行带参数的SQL语句

从表中去除重复行数据

1. 如果有ID字段，就是具有唯一性的字段 

 -- group  by  子句后跟的字段就是你用来判断重复的条件，如只有col1，那么只要col1字段内容相同即表示记录相同。
 delete   table  tableName 
 where   id   not   in   (   select   max(id)   from   table   group   by   col1,col2,col3...   )

2. 如果是判断所有字段也可以这样  ，【对于表中的指定的字段的进行检查是否相同】

select   *   into   #temp  from   tablename    group   by   id1,id2,....    
delete    tablename      
insert   into   table  select   *   from   #temp 
drop   table   #temp

3. 首先去重复，再获取N*1条数据插入到临时表中，【对于表中的所有字段的进行检查是否相同】，再将原表的数据删除，然后将临时表的数据插入到原表，最后删除临时表。

select   distinct   *   into   #temp   from   tablename      
delete   tablename      
go    
insert   tablename   select   *   from   #temp    
go    
drop   table   #temp

4. 没有ID的情况

select   identity(int,1,1)   as   id,*   into   #temp   from   tabel    
delect   #   where   id   not   in   (    
select   max(id)   from   #   group   by   col1,col2,col3...)    
delect   table    
inset   into   table(...)    
select   .....   from   #temp

5. col1+','+col2+','...col5 联合主键

select * from table where col1+','+col2+','...col5 in (
select max(col1+','+col2+','...col5) from table
where having count(*)>1
group by col1,col2,col3,col4
)
-- group   by   子句后跟的字段就是你用来判断重复的条件，如只有col1，那么只要col1字段内容相同即表示记录相同。  

 6. 使用自增列

select   identity(int,1,1)   as   id,*   into   #temp   from   tabel     
select   *   from     #temp   where   id   in   (     
select   max(id)   from   #emp   where   having   count(*)>1   group   by   col1,col2,col3...)   　　

逗号分隔字符串转数据表行

1. 使用CHARINDEX和SUBSTRING函数

CREATE FUNCTION dbo.splitstring
    (
      @stringToSplit VARCHAR(MAX)
    )
RETURNS @returnList TABLE ( [Name] [nvarchar](500) )
AS 
    BEGIN
 
        DECLARE @name NVARCHAR(255)
        DECLARE @pos INT
 
        WHILE CHARINDEX(',', @stringToSplit) > 0 
            BEGIN
                SELECT  @pos = CHARINDEX(',', @stringToSplit) 
                SELECT  @name = SUBSTRING(@stringToSplit, 1, @pos - 1)
 
                INSERT  INTO @returnList
                        SELECT  @name
 
                SELECT  @stringToSplit = SUBSTRING(@stringToSplit, @pos + 1,
                                                   LEN(@stringToSplit) - @pos)
            END
 
        INSERT  INTO @returnList
                SELECT  @stringToSplit
 
        RETURN
    END

2. 使用XML-Method[SQL Server 2005+]

CREATE FUNCTION [dbo].[ufnGetSplitValues]
    (
      @StringValues NVARCHAR(4000),
      @Delimiter CHAR(1)
    )
RETURNS TABLE
AS
RETURN
    (
        SELECT LTRIM(RTRIM(Split.a.value('.', 'NVARCHAR(100)'))) 'Value'
        FROM 
        (    
             SELECT CAST ('<M>' + REPLACE(@StringValues, @Delimiter, '</M><M>') + '</M>' AS XML) AS Data           
        ) AS A
        CROSS APPLY Data.nodes ('/M') AS Split(a)  
    )
GO

3. STRING_SPLIT()函数[SQL Server 2016 +]

SELECT * FROM STRING_SPLIT('a,b,cd', ',');
 
/* result:
 
    value
    --------
    a
    b
    cd
*/　　

4. 参考资料

• https://sqlperformance.com/2016/03/t-sql-queries/string-split
• http://stackoverflow.com/questions/5493510/turning-a-comma-separated-string-into-individual-rows

跨DB/Server执行SP[分布式事务]

USE Database1
GO

-- 如果不加SET FMTONLY OFF，在执行时可能会出现分布式事务异常
SELECT name, age, sex INTO #Persons FROM OPENQUERY(LinkedServer,
 'SET FMTONLY OFF  EXEC [database2].[dbo].uspGetPersonList')

在OpenQuery中执行带参数的SQL语句

DECLARE @Sql VARCHAR(1000)
DECLARE @organizationID VARCHAR(10)
SELECT @organizationID = (SELECT ORGANIZATION_ID FROM MYORGS WHERE ORGANIZATION_NAME = 'MMT')
SET @Sql = 'SELECT * from tableName where organization_id ='+@organizationID
SET @Sql = 'SELECT * FROM OPENQUERY(LinkedServerName, ''' + REPLACE(@Sql, '''', '''''') + ''')'
EXEC(@Sql)