SQL语句技巧

SQL语句技巧

1 行列相关1.1  行列转换--普通

 

假设有张学生成绩表(CJ)如下

Name Subject Result

张三 语文 80

张三 数学 90

张三 物理 85

李四 语文 85

李四 数学 92

李四 物理 82

 

想变成

姓名 语文 数学 物理

张三 80 90 85

李四 85 92 82

 

declare @sql varchar(4000)

set @sql = 'select Name'

select @sql = @sql + ',sum(case Subject when '''+Subject+''' then Result end) ['+Subject+']'

from (select distinct Subject from CJ) as a

select @sql = @sql+' from test group by name'

exec(@sql)

 

1.2  行列转换--合并

 

有表A,

id pid

1 1

1 2

1 3

2 1

2 2

3 1

如何化成表B:

id pid

1 1,2,3

2 1,2

3 1

 

创建一个合并的函数

create function fmerg(@id int)

returns varchar(8000)

as

begin

declare @str varchar(8000)

set @str=''

select @str=@str+','+cast(pid as varchar) from 表A where id=@id

set @str=right(@str,len(@str)-1)

return(@str)

End

go

 

--调用自定义函数得到结果

select distinct id,dbo.fmerg(id) from 表A

 

1.3 示例

select * from v_temp

上面的视图结果如下:

user_name role_name

-------------------------

系统管理员 管理员

feng 管理员

feng 一般用户

test 一般用户 

想把结果变成这样:

user_name role_name

---------------------------

系统管理员 管理员

feng 管理员,一般用户

test 一般用户

===================

create table a_test(name varchar(20),role2 varchar(20))

insert into a_test values('李','管理員')

insert into a_test values('張','管理員')

insert into a_test values('張','一般用戶')

insert into a_test values('常','一般用戶')

 

create function join_str(@content varchar(100))

returns varchar(2000)

as

begin

declare @str varchar(2000)

set @str=''

select @str=@str+','+rtrim(role2) from a_test where [name]=@content

select @str=right(@str,len(@str)-1)

return @str

end

go

 

--调用：

select [name],dbo.join_str([name]) role2 from a_test group by [name]

 

--select distinct name,dbo.uf_test(name) from a_test

 

2比较结构相同的两表

结构相同的两表，一表有记录3万条左右，一表有记录2万条左右，我怎样快速查找两表的不同记录？

============================ 

给你一个测试方法，从northwind中的orders表取数据。

select * into n1 from orders

select * into n2 from orders

 

select * from n1

select * from n2

 

--添加主键，然后修改n1中若干字段的若干条

alter table n1 add constraint pk_n1_id primary key (OrderID)

alter table n2 add constraint pk_n2_id primary key (OrderID)

 

select OrderID from (select * from n1

union

select * from n2) a group by OrderID having count(*) > 1

 

应该可以，而且将不同的记录的ID显示出来。

下面的适用于双方记录一样的情况，

 

select * from n1 where orderid in

(

select OrderID from (select * from n1

union

select * from n2) a group by OrderID having count(*) > 1

)

至于双方互不存在的记录是比较好处理的

--删除n1,n2中若干条记录

delete from n1 where orderID in ('10728','10730')

delete from n2 where orderID in ('11000','11001')

 

--*************************************************************

-- 双方都有该记录却不完全相同 网管u家u.bitsCN.com

select * from n1 where orderid in

(

select OrderID from (select * from n1

union

select * from n2) a group by OrderID having count(*) > 1

)

union

--n2中存在但在n1中不存的在10728,10730

select * from n1 where OrderID not in (select OrderID from n2)

union

--n1中存在但在n2中不存的在11000,11001

select * from n2 where OrderID not in (select OrderID from n1)

 

3 四种方法取表里n到m条纪录：

 

1.

select top m * into 临时表(或表变量) from tablename order by columnname -- 将top m笔插入

set rowcount n

select * from 表变量 order by columnname desc

 

 

2.

select top n * from

(select top m * from tablename order by columnname) a

order by columnname desc

 

 

3.如果tablename里没有其他identity列，那么：

select identity(int) id0,* into #temp from tablename

 

取n到m条的语句为：

select * from #temp where id0 >=n and id0 <= m

 

如果你在执行select identity(int) id0,* into #temp from tablename这条语句的时候报错,那是因为你的DB中间的select into/bulkcopy属性没有打开要先执行： 网管联盟bitsCN@com

exec sp_dboption 你的DB名字,'select into/bulkcopy',true

 

 

4.如果表里有identity属性，那么简单：

select * from tablename where identitycol between n and m

5.如何删除一个表中重复的记录？

create table a_dist(id int,name varchar(20))

 

insert into a_dist values(1,'abc')

insert into a_dist values(1,'abc')

insert into a_dist values(1,'abc')

insert into a_dist values(1,'abc')

 

exec up_distinct 'a_dist','id'

 

select * from a_dist

 

create procedure up_distinct(@t_name varchar(30),@f_key varchar(30))

--f_key表示是分組字段﹐即主鍵字段

as

begin

declare @max integer,@id varchar(30) ,@sql varchar(7999) ,@type integer

select @sql = 'declare cur_rows cursor for select '+@f_key+' ,count(*) from ' +@t_name +' group by ' +@f_key +' having count(*) > 1'

exec(@sql)

open cur_rows

fetch cur_rows into @id,@max

while @@fetch_status=0

begin

select @max = @max -1

set rowcount @max

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select @type = xtype from syscolumns where id=object_id(@t_name) and name=@f_key

if @type=56

select @sql = 'delete from '+@t_name+' where ' + @f_key+' = '+ @id

if @type=167

select @sql = 'delete from '+@t_name+' where ' + @f_key+' = '+''''+ @id +''''

exec(@sql)

fetch cur_rows into @id,@max

end

close cur_rows

deallocate cur_rows

set rowcount 0

end

 

select * from systypes

select * from syscolumns where id = object_id('a_dist')

 

4 查询数据的最大排序问题（只能用一条语句写）

CREATE TABLE hard (qu char (11) ,co char (11) ,je numeric(3, 0))

 

insert into hard values ('A','1',3)

insert into hard values ('A','2',4)

insert into hard values ('A','4',2)

insert into hard values ('A','6',9)

insert into hard values ('B','1',4)

insert into hard values ('B','2',5)

insert into hard values ('B','3',6)

insert into hard values ('C','3',4)

insert into hard values ('C','6',7)

insert into hard values ('C','2',3)

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要求查询出来的结果如下：

 

qu co je

----------- ----------- -----

A 6 9

A 2 4

B 3 6

B 2 5

C 6 7

C 3 4

 

 

就是要按qu分组，每组中取je最大的前2位！！

而且只能用一句sql语句！！！

select * from hard a where je in (select top 2 je from hard b where a.qu=b.qu order by je)

5 求删除重复记录的sql语句

怎样把具有相同字段的纪录删除，只留下一条。

例如，表test里有id,name字段

如果有name相同的记录 只留下一条，其余的删除。

name的内容不定，相同的记录数不定。

 

==============================

A:一个完整的解决方案：

 

将重复的记录记入temp1表:

select [标志字段id],count(*) into temp1 from [表名]

group by [标志字段id]

having count(*)>1

 

2、将不重复的记录记入temp1表:

insert temp1

select [标志字段id],count(*) from [表名]

group by [标志字段id]

having count(*)=1

 

3、作一个包含所有不重复记录的表：

select * into temp2 from [表名]

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where 标志字段id in(select 标志字段id from temp1)

 

4、删除重复表:

delete [表名]

 

5、恢复表：

insert [表名]

select * from temp2

 

6、删除临时表:

drop table temp1

drop table temp2

================================

B:

create table a_dist(id int,name varchar(20))

 

insert into a_dist values(1,'abc')

insert into a_dist values(1,'abc')

insert into a_dist values(1,'abc')

insert into a_dist values(1,'abc')

 

exec up_distinct 'a_dist','id'

 

select * from a_dist

 

create procedure up_distinct(@t_name varchar(30),@f_key varchar(30))

--f_key表示是分組字段﹐即主鍵字段

as

begin

declare @max integer,@id varchar(30) ,@sql varchar(7999) ,@type integer

select @sql = 'declare cur_rows cursor for select '+@f_key+' ,count(*) from ' +@t_name +' group by ' +@f_key +' having count(*) > 1'

exec(@sql)

open cur_rows

fetch cur_rows into @id,@max

while @@fetch_status=0

 

 

 

begin

select @max = @max -1

set rowcount @max

select @type = xtype from syscolumns where id=object_id(@t_name) and name=@f_key

if @type=56

select @sql = 'delete from '+@t_name+' where ' + @f_key+' = '+ @id

if @type=167

select @sql = 'delete from '+@t_name+' where ' + @f_key+' = '+''''+ @id +''''

exec(@sql)

fetch cur_rows into @id,@max

end

close cur_rows

deallocate cur_rows

set rowcount 0

end

 

select * from systypes

select * from syscolumns where id = object_id('a_dist')

 

 

6 取得一个数据表的所有列名

 

方法如下：先从SYSTEMOBJECT系统表中取得数据表的SYSTEMID,然后再SYSCOLUMN表中取得该数据表的所有列名。

SQL语句如下：

declare @objid int,@objname char(40)

set @objname = 'tablename'

select @objid = id from sysobjects where id = object_id(@objname)

select 'Column_name' = name from syscolumns where id = @objid order by colid

 

是不是太简单了？ 呵呵 不过经常用阿.

 

7 通过SQL语句来更改用户的密码

 

修改别人的,需要sysadmin role

EXEC sp_password NULL, 'newpassword', 'User'

 

如果帐号为SA执行EXEC sp_password NULL, 'newpassword', sa

 

8 怎么判断出一个表的哪些字段不允许为空？

 

select COLUMN_NAME from INFORMATION_SCHEMA.COLUMNS where IS_NULLABLE='NO' and TABLE_NAME=tablename

 

9 如何在数据库里找到含有相同字段的表？

a. 查已知列名的情况 网管朋友网www_bitscn_net

SELECT b.name as TableName,a.name as columnname

From syscolumns a INNER JOIN sysobjects b

ON a.id=b.id

AND b.type='U'

AND a.name='你的字段名字'

 

b. 未知列名查所有在不同表出现过的列名

Select o.name As tablename,s1.name As columnname

From syscolumns s1, sysobjects o

Where s1.id = o.id

And o.type = 'U'

And Exists (

Select 1 From syscolumns s2

Where s1.name = s2.name

And s1.id <> s2.id

)

 

10 查询第xxx行数据

 

假设id是主键：

select *

from (select top xxx * from yourtable) aa

where not exists(select 1 from (select top xxx-1 * from yourtable) bb where aa.id=bb.id)

 

如果使用游标也是可以的

fetch absolute [number] from [cursor_name]

行数为绝对行数

 

11 SQL Server日期计算

a. 一个月的第一天

SELECT DATEADD(mm, DATEDIFF(mm,0,getdate()), 0)

b. 本周的星期一

SELECT DATEADD(wk, DATEDIFF(wk,0,getdate()), 0)

c. 一年的第一天 网管u家www.bitscn.net

SELECT DATEADD(yy, DATEDIFF(yy,0,getdate()), 0)

d. 季度的第一天

SELECT DATEADD(qq, DATEDIFF(qq,0,getdate()), 0)

e. 上个月的最后一天

SELECT dateadd(ms,-3,DATEADD(mm, DATEDIFF(mm,0,getdate()), 0))

f. 去年的最后一天

SELECT dateadd(ms,-3,DATEADD(yy, DATEDIFF(yy,0,getdate()), 0))

g. 本月的最后一天

SELECT dateadd(ms,-3,DATEADD(mm, DATEDIFF(m,0,getdate())+1, 0))

h. 本月的第一个星期一

select DATEADD(wk, DATEDIFF(wk,0,

dateadd(dd,6-datepart(day,getdate()),getdate())

), 0)

i. 本年的最后一天

SELECT dateadd(ms,-3,DATEADD(yy, DATEDIFF(yy,0,getdate())+1, 0))。

 

12 获取表结构

[把 'sysobjects' 替换 成 'tablename' 即可]

 

SELECT CASE IsNull(I.name, '')

When '' Then ''

Else '*'

End as IsPK,

Object_Name(A.id) as t_name,

A.name as c_name,

IsNull(SubString(M.text, 1, 254), '') as pbc_init,

T.name as F_DataType,

CASE IsNull(TYPEPROPERTY(T.name, 'Scale'), '')

WHEN '' Then Cast(A.prec as varchar)

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ELSE Cast(A.prec as varchar) + ',' + Cast(A.scale as varchar)

END as F_Scale,

A.isnullable as F_isNullAble

FROM Syscolumns as A

JOIN Systypes as T

ON (A.xType = T.xUserType AND A.Id = Object_id('sysobjects') )

LEFT JOIN ( SysIndexes as I

JOIN Syscolumns as A1

ON ( I.id = A1.id and A1.id = object_id('sysobjects') and (I.status & 0x800) = 0x800 AND A1.colid <= I.keycnt) )

ON ( A.id = I.id AND A.name = index_col('sysobjects', I.indid, A1.colid) )

LEFT JOIN SysComments as M

ON ( M.id = A.cdefault and ObjectProperty(A.cdefault, 'IsConstraint') = 1 )

ORDER BY A.Colid ASC

 

 

13 提取数据库内所有表的字段详细说明的SQL语句

SELECT

(case when a.colorder=1 then d.name else '' end) N'表名',

a.colorder N'字段序号',

a.name N'字段名',

(case when COLUMNPROPERTY( a.id,a.name,'IsIdentity')=1 then '√'else ''

end) N'标识',

(case when (SELECT count(*)

FROM sysobjects

WHERE (name in 网管u家u.bitsCN.com

(SELECT name

FROM sysindexes

WHERE (id = a.id) AND (indid in

(SELECT indid

FROM sysindexkeys

WHERE (id = a.id) AND (colid in

(SELECT colid

FROM syscolumns

WHERE (id = a.id) AND (name = a.name))))))) AND

(xtype = 'PK'))>0 then '√' else '' end) N'主键',

b.name N'类型',

a.length N'占用字节数',

COLUMNPROPERTY(a.id,a.name,'PRECISION') as N'长度',

isnull(COLUMNPROPERTY(a.id,a.name,'Scale'),0) as N'小数位数',

(case when a.isnullable=1 then '√'else '' end) N'允许空',

isnull(e.text,'') N'默认值',

isnull(g.[value],'') AS N'字段说明'

FROM syscolumns a

left join systypes b

on a.xtype=b.xusertype

inner join sysobjects d

on a.id=d.id and d.xtype='U' and d.name<>'dtproperties'

left join syscomments e

on a.cdefault=e.id

left join sysproperties g

on a.id=g.id AND a.colid = g.smallid

order by object_name(a.id),a.colorder

 

14 快速获取表test的记录总数

 

快速获取表test的记录总数:

select rows from sysindexes where id = object_id(‘test’) and indid in (0,1)