最近在MySQL中遇到分组排序查询时,突然发现MySQL中没有row_number() over(partition by colname)这样的分组排序。
并且由于MySQL中没有类似于SQL Server中的row_number()、rank()、dense_rank()等排名函数,所有找到以下实现方法,在此简单记录一下。
首先创建一个表并插入测试数据。
create table demo.Student ( ID int(11) NOT NULL AUTO_INCREMENT, StuNo varchar(32) NOT NULL, StuName varchar(10) NOT NULL, StuAge int(11) DEFAULT NULL, PRIMARY KEY (ID) ) engine=innodb auto_increment=1 default charset=utf8 collate=utf8_general_ci; insert into demo.Student(StuNo,StuName,StuAge) values(‘A001‘,‘小明‘,22); insert into demo.Student(StuNo,StuName,StuAge) values(‘A005‘,‘小李‘,23); insert into demo.Student(StuNo,StuName,StuAge) values(‘A007‘,‘小红‘,24); insert into demo.Student(StuNo,StuName,StuAge) values(‘A003‘,‘小明‘,22); insert into demo.Student(StuNo,StuName,StuAge) values(‘A002‘,‘小李‘,23); insert into demo.Student(StuNo,StuName,StuAge) values(‘A004‘,‘小红‘,24); insert into demo.Student(StuNo,StuName,StuAge) values(‘A006‘,‘小王‘,25); select * from demo.Student;
测试数据如下:
实现row_number()排名函数,按学号(StuNo)排序。
-- @row_number:=0,设置变量@row_number的初始值为0。 -- @row_number:[email protected]_number+1,累加@row_number的值。 select ID,StuNo,StuName,StuAge,@row_number:[email protected]_number+1 as row_number from demo.Student a, ( select @row_number:=0 ) b order by StuNo asc;
结果如下:
实现rank()排名函数,按学生年龄(StuAge)排序。
-- @StuAge:=null,设置变量@StuAge的初始值为null -- @rank:=0,设置变量@rank的初始值为0 -- @inRank:=1,设置变量@inRank的初始值为1 -- if(@StuAge=StuAge,@rank,@rank:[email protected]),指定排序列的值不变时,@rank的值不变;指定排序列的值变化时,@rank的值跳变为@inRank内部计数的值 -- @inRank:[email protected]+1,每一行自增1,用于实现内部计数 select t.ID,t.StuNo,t.StuName,t.StuAge,t.row_rank from ( select ID,StuNo,StuName,StuAge,if(@StuAge=StuAge,@rank,@rank:[email protected]) as row_rank,@inRank:[email protected]+1,@StuAge:=StuAge from demo.Student a, ( select @StuAge:=null,@rank:=0,@inRank:=1 ) b order by StuAge asc ) t;
结果如下:
实现dense_rank()排名函数,按学生年龄(StuAge)排序。
-- @StuAge:=null,设置变量@StuAge的初始值为null -- @rank:=0,设置变量@rank的初始值为0 -- if(@StuAge=StuAge,@rank,@rank:[email protected]+1),指定排序列的值不变时,@rank的值不变;指定排序列的值变化时,@rank的值自增1 select t.ID,t.StuNo,t.StuName,t.StuAge,t.row_rank from ( select ID,StuNo,StuName,StuAge,if(@StuAge=StuAge,@rank,@rank:[email protected]+1) as row_rank,@StuAge:=StuAge from demo.Student a, ( select @StuAge:=null,@rank:=0 ) b order by StuAge asc ) t;
结果如下:
实现row_number() over(partition by colname order by colname)分组排名函数,按学生年龄(StuAge)分组排序。
-- @StuAge:=null,设置变量@StuAge的初始值为null -- @row_number:=0,设置变量@row_number的初始值为0 -- if(@StuAge=StuAge,@row_number:[email protected]_number+1,@row_number:=1),指定排序列的值不变时,@row_number的值自增1;指定排序列的值变化时,@row_number的值等于1 select t.ID,t.StuNo,t.StuName,t.StuAge,t.row_number from ( select ID,StuNo,StuName,StuAge,if(@StuAge=StuAge,@row_number:[email protected]_number+1,@row_number:=1) as row_number,@StuAge:=StuAge from demo.Student a, ( select @StuAge:=null,@row_number:=0 ) b order by StuAge asc ) t;
结果如下:
实现分组聚合字符串,即把指定列的值拼成字符串。
在SQL Server中时利用了中间变量实现,现在在MySQL中就比较简单了。
MySQL提供了一个group_concat()函数,可以把指定列的值拼成一个字符串,并可以按指定排序方式拼成字符,之间用逗号隔开。如下示例:
select group_concat(StuNo order by StuNo asc) as column1,group_concat(StuNo order by ID asc) as column2 from demo.Student
结果如下:
select StuName,group_concat(StuNo order by StuNo asc) as column1,concat(‘"‘,group_concat(StuNo order by StuNo asc),‘"‘) as column2 from demo.Student group by StuName order by StuAge
结果如下:
原文地址:https://www.cnblogs.com/asdyzh/p/9818761.html
时间: 2024-11-08 13:21:13