分类： Mysql/postgreSQL
2008-05-19 16:24:11
10.SQL语句技巧
1、一个SQL语句的问题:行列转换
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、求助！快速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
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：
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
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')
