MySQL (C API)VC实例及代码下载

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)

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？

如何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：

1)、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')

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