sql技巧

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表示是分组字段﹐即主键字段

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')

 

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)

 

 

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)

 

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。

有没有这样的sql语句？

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

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] 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表示是分组字段﹐即主键字段

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')

 

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)

 

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

 

 

如何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

 

或

 

SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME ='users'

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

 

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

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

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'

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

)

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

 

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

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))。

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)

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

 

 

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

(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

 

快速获取表test的记录总数[对大容量表非常有效]

 

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)

 

update 2 set KHXH=(ID+1)\2 2行递增编号

update [23] set id1 = 'No.'+right('00000000'+id,6) where id not like 'No%' //递增

update [23] set id1= 'No.'+right('00000000'+replace(id1,'No.',''),6) //补位递增

delete from [1] where (id%2)=1

奇数

替换表名字段

update [1] set domurl = replace(domurl,'Upload/Imgswf/','Upload/Photo/') where domurl like '%Upload/Imgswf/%'

截位

SELECT LEFT(表名, 5)

 

截位

SELECT LEFT(表名, 5)