SQL语句大全【第二部分】技巧+经典案例

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2020-06-1313:06:00 评论 249 6444字
摘要

SQL作为数据分析师在日常工作中的必备技能,直接影响着分析师们的工作效率,用好学好SQL会使工作效率大幅度提升,本文分享了SQL的基础与进阶技能。

一.技巧

1.1=1,1=2的使用,在SQL语句组合时用的较多

"where 1=1" 是表示选择全部 "where 1=2"全部不选。

如:

if @strWhere !=""

begin

set @strSQL = "select count(*) as Total from [" + @tblName + "] where " + @strWhere

end

else

begin

set @strSQL = "select count(*) as Total from [" + @tblName + "]"

end

我们可以直接写成

错误!未找到目录项。

set @strSQL = "select count(*) as Total from [" + @tblName + "] where 1=1 and "+ @strWhere

2.收缩数据库

重建索引

DBCC REINDEX

DBCC INDEXDEFRAG

收缩数据和日志

DBCC SHRINKDB

DBCC SHRINKFILE

3.压缩数据库

dbcc shrinkdatabase(dbname)

4.转移数据库给新用户以已存在用户权限

exec sp_change_users_login "update_one","newname","oldname"

go

5.检查备份集

RESTORE VERIFYONLY from disk="E:dvbbs.bak"

6.修复数据库

ALTER DATABASE [dvbbs] SET SINGLE_USER

GO

DBCC CHECKDB("dvbbs",repair_allow_data_loss) WITH TABLOCK

GO

ALTER DATABASE [dvbbs] SET MULTI_USER

GO

7.日志清除

SET NOCOUNT ON

DECLARE @LogicalFileName sysname,

@MaxMinutes INT,

@NewSize INT

USE tablename -- 要操作的数据库名

SELECT @LogicalFileName = "tablename_log", -- 日志文件名

@MaxMinutes = 10, -- Limit on time allowed to wrap log.

@NewSize = 1 -- 你想设定的日志文件的大小(M)

Setup / initialize

DECLARE @OriginalSize int

SELECT @OriginalSize = size

FROM sysfiles

WHERE name = @LogicalFileName

SELECT "Original Size of " + db_name() + " LOG is " +

CONVERT(VARCHAR(30),@OriginalSize) + " 8K pages or " +

CONVERT(VARCHAR(30),(@OriginalSize*8/1024)) + "MB"

FROM sysfiles

WHERE name = @LogicalFileName

CREATE TABLE DummyTrans

(DummyColumn char (8000) not null)

DECLARE @Counter INT,

@StartTime DATETIME,

@TruncLog VARCHAR(255)

SELECT @StartTime = GETDATE(),

@TruncLog = "BACKUP LOG " + db_name() + " WITH TRUNCATE_ONLY"

DBCC SHRINKFILE (@LogicalFileName, @NewSize)

EXEC (@TruncLog)

-- Wrap the log if necessary.

WHILE @MaxMinutes > DATEDIFF (mi, @StartTime, GETDATE()) -- time has not expired

AND @OriginalSize = (SELECT size FROM sysfiles WHERE name = @LogicalFileName)

AND (@OriginalSize * 8 /1024) > @NewSize

BEGIN -- Outer loop.

SELECT @Counter = 0

WHILE ((@Counter < @OriginalSize / 16) AND (@Counter < 50000))

BEGIN -- update

INSERT DummyTrans VALUES ("Fill Log") DELETE DummyTrans

SELECT @Counter = @Counter + 1

END

EXEC (@TruncLog)

END

SELECT "Final Size of " + db_name() + " LOG is " +

CONVERT(VARCHAR(30),size) + " 8K pages or " +

CONVERT(VARCHAR(30),(size*8/1024)) + "MB"

FROM sysfiles

WHERE name = @LogicalFileName

DROP TABLE DummyTrans

SET NOCOUNT OFF

8.更改某个表

exec sp_changeobjectowner "tablename","dbo"

9.存储更改全部表

CREATE PROCEDURE dbo.User_ChangeObjectOwnerBatch

@OldOwner as NVARCHAR(128),

@NewOwner as NVARCHAR(128)

AS

DECLARE @Name as NVARCHAR(128)

DECLARE @Owner as NVARCHAR(128)

DECLARE @OwnerName as NVARCHAR(128)

DECLARE curObject CURSOR FOR

select "Name" = name,

"Owner" = user_name(uid)

from sysobjects

where user_name(uid)=@OldOwner

order by name

OPEN curObject

FETCH NEXT FROM curObject INTO @Name, @Owner

WHILE(@@FETCH_STATUS=0)

BEGIN

if @Owner=@OldOwner

begin

set @OwnerName = @OldOwner + "." + rtrim(@Name)

exec sp_changeobjectowner @OwnerName, @NewOwner

end

-- select @name,@NewOwner,@OldOwner

FETCH NEXT FROM curObject INTO @Name, @Owner

END

close curObject

deallocate curObject

GO

10.SQL SERVER中直接循环写入数据

declare @i int

set @i=1

while @i<30

begin

insert into test (userid) values(@i)

set @i=@i+1

end

案例:

有如下表,要求就裱中所有沒有及格的成績,在每次增長0.1的基礎上,使他們剛好及格:

Name score

Zhangshan 80

Lishi 59

Wangwu 50

Songquan 69

while((select min(score) from tb_table)<60)

begin

update tb_table set score =score*1.01

where score<60

if (select min(score) from tb_table)>60

break

else

continue

end

二.经典

1.按姓氏笔画排序

Select * From TableName Order By CustomerName Collate Chinese_PRC_Stroke_ci_as //从少到多

2.数据库加密

select encrypt("原始密码")

select pwdencrypt("原始密码")

select pwdcompare("原始密码","加密后密码") = 1--相同;否则不相同 encrypt("原始密码")

select pwdencrypt("原始密码")

select pwdcompare("原始密码","加密后密码") = 1--相同;否则不相同

3.取回表中字段

declare @list varchar(1000),

@sql nvarchar(1000)

select @list=@list+","+b.name from sysobjects a,syscolumns b where a.id=b.id and a.name="表A"

set @sql="select "+right(@list,len(@list)-1)+" from 表A"

exec (@sql)

4.查看硬盘分区

EXEC master..xp_fixeddrives

5.比较A,B表是否相等

if (select checksum_agg(binary_checksum(*)) from A)

=

(select checksum_agg(binary_checksum(*)) from B)

print "相等"

else

print "不相等"

6.杀掉所有的事件探察器进程

DECLARE hcforeach CURSOR GLOBAL FOR SELECT "kill "+RTRIM(spid) FROM master.dbo.sysprocesses

WHERE program_name IN("SQL profiler",N"SQL 事件探查器")

EXEC sp_msforeach_worker "?"

7.记录搜索

开头到N条记录

Select Top N * From 表

N到M条记录(要有主索引ID)

Select Top M-N * From 表 Where ID in (Select Top M ID From 表) Order by ID Desc

N到结尾记录

Select Top N * From 表 Order by ID Desc

案例

例1:一张表有一万多条记录,表的第一个字段 RecID 是自增长字段, 写一个SQL语句, 找出表的第31到第40个记录。

select top 10 recid from A where recid not in(select top 30 recid from A)

分析:如果这样写会产生某些问题,如果recid在表中存在逻辑索引。

select top 10 recid from A where……是从索引中查找,而后面的select top 30 recid from A则在数据表中查找,这样由于索引中的顺序有可能和数据表中的不一致,这样就导致查询到的不是本来的欲得到的数据。

解决方案

1)如果该字段不是自增长,就会出现问题

order by select top 30 recid from A order by ricid

2)在那个子查询中也加条件

select top 30 recid from A where recid>-1

例2:查询表中的最后一条记录,并不知道这个表共有多少数据,以及表结构。

set @s = "select top 1 * from T where pid not in (select top " + str(@count-1) + " pid from T)"

print @s exec sp_executesql @s

9.获取当前数据库中的所有用户表

select Name from sysobjects where xtype="u" and status>=0

10.获取某一个表的所有字段

select name from syscolumns where id=object_id("表名")

select name from syscolumns where id in (select id from sysobjects where type = "u" and name = "表名")

两种方式的效果相同

11.查看与某一个表相关的视图、存储过程、函数

select a.* from sysobjects a, syscomments b where a.id = b.id and b.text like "%表名%"

12.查看当前数据库中所有存储过程

select name as 存储过程名称 from sysobjects where xtype="P"

13.查询用户创建的所有数据库

select * from master..sysdatabases D where sid not in(select sid from master..syslogins where name="sa")

或者

select dbid, name AS DB_NAME from master..sysdatabases where sid <> 0x01

14.查询某一个表的字段和数据类型

select column_name,data_type from information_schema.columns

where table_name = "表名"select column_name,data_type from information_schema.columns

where table_name = "表名"

15.不同服务器数据库之间的数据操作

创建链接服务器

exec sp_addlinkedserver "ITSV ", " ", "SQLOLEDB ", "远程服务器名或ip地址 "

exec sp_addlinkedsrvlogin "ITSV ", "false ",null, "用户名 ", "密码 " 

查询示例

select * from ITSV.数据库名.dbo.表名

导入示例

select * into 表 from ITSV.数据库名.dbo.表名

以后不再使用时删除链接服务器

exec sp_dropserver "ITSV ", "droplogins "

连接远程/局域网数据(openrowset/openquery/opendatasource)

1)openrowset

查询示例

select * from openrowset( "SQLOLEDB ", "sql服务器名 "; "用户名 "; "密码 ",数据库名.dbo.表名)

生成本地表

select * into 表 from openrowset( "SQLOLEDB ", "sql服务器名 "; "用户名 "; "密码 ",数据库名.dbo.表名)

把本地表导入远程表

insert openrowset( "SQLOLEDB ", "sql服务器名 "; "用户名 "; "密码 ",数据库名.dbo.表名)

select *from 本地表

更新本地表

update b

set b.列A=a.列A

from openrowset( "SQLOLEDB ", "sql服务器名 "; "用户名 "; "密码 ",数据库名.dbo.表名)as a inner join 本地表 b

on a.column1=b.column1

2)openquery用法需要创建一个连接

首先创建一个连接创建链接服务器

exec sp_addlinkedserver "ITSV ", " ", "SQLOLEDB ", "远程服务器名或ip地址 "

查询

select * FROM openquery(ITSV, "SELECT * FROM 数据库.dbo.表名 ")

把本地表导入远程表

insert openquery(ITSV, "SELECT * FROM 数据库.dbo.表名 ")

select * from 本地表

更新本地表

update b

set b.列B=a.列B

FROM openquery(ITSV, "SELECT * FROM 数据库.dbo.表名 ") as a

inner join 本地表 b on a.列A=b.列A

3)opendatasource/openrowset

SELECT *

FROM opendatasource( "SQLOLEDB ", "Data Source=ip/ServerName;User ID=登陆名;Password=密码 " ).test.dbo.roy_ta

把本地表导入远程表

insert opendatasource( "SQLOLEDB ", "Data Source=ip/ServerName;User ID=登陆名;Password=密码 ").数据库.dbo.表名

select * from 本地表

End.作者:yubinfeng来源:博客园http://www.cnblogs.com/yubinfeng/archive/2010/11/02/1867386.html本文为转载分享,如侵权请联系后台删除

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