如何对后续行进行分组(基于条件),然后对它们进行计数[MySQL]? [英] How to group subsequent rows (based on a criteria) and then count them [MySQL]?
问题描述
假设我有这样的表(按日期排序):
id |名称|类型| date
1 | A | 1 | 01-08-2012
2 | A | 2 | 01-08-2012
3 | B | 1 | 02-09-2012
4 | A | 1 | 01-10-2012
5 | A | 4 | 01-10-2012
6 | A | 5 | 02-10-2012
我想对具有相同name值和计数的后续行进行分组他们:
name | count
A | 2
B | 1
A | 3
我在想写一个存储过程和使用游标,但我也想知道,如果有一个更简单的解决方案,例如使用嵌套的SELECT等。
我的问题非常类似于:如何对数组进行分组和计数,但是一个涉及PHP。
表结构,我创建了自己的测试,它是:
create table abc(id int,name varchar(20),type int);
insert into abc values
(1,'A',1),
(2,'A',2),
(3,'B' ,
(4,'A',1),
(5,'A',4),
(6,'A',5) / code>
查询结束是这样的:
code> set @a:='';
set @counter:= 1;
set @groupby:= 0;
select *,count(REPEATED)from(select name,if(@ a = name,@ counter:= @ counter + 1,@ counter:= 1)as rep,if(@ counter = 1,@ groupby := @ groupby + 1,@ groupby)as a repeated,@ a:= name type from abc)as t group by repeated
b $ b
您可以看到它在 SQLFIDDLE 中有效,如果您有任何问题让我知道。
在SQLFIDDLE
Let's say I have such a table (ordered by date):
id | name | type | date
1 | A | 1 | 01-08-2012
2 | A | 2 | 01-08-2012
3 | B | 1 | 02-09-2012
4 | A | 1 | 01-10-2012
5 | A | 4 | 01-10-2012
6 | A | 5 | 02-10-2012
I want to group subsequent rows that have the same 'name' value and count them:
name | count
A | 2
B | 1
A | 3
I was thinking about writing a stored procedure and using cursors, but I was also wondering, if there's a simpler solution, for example using nested SELECTs, etc.
My question is very similar to: how to group array and count them, but that one concerns PHP.
To do that I used a couple of variables, the table structure, I created my own just for testing and it's:
create table abc (id int, name varchar(20),type int);
insert into abc values
( 1 , 'A' , 1 ),
( 2 , 'A' , 2 ),
( 3 , 'B' , 1 ),
( 4 , 'A' , 1 ),
( 5 , 'A' , 4 ),
( 6 , 'A' , 5 )
the query ended being like this:
set @a:='';
set @counter:=1;
set @groupby:=0;
select *,count(REPEATED) from (select name,if(@a=name,@counter:=@counter+1,@counter:=1) as rep,if(@counter=1,@groupby:=@groupby+1,@groupby) as repeated,@a:=name type from abc) as t group by repeated
you can see it works in SQLFIDDLE if you have any question let me know.
In the SQLFIDDLE
这篇关于如何对后续行进行分组(基于条件),然后对它们进行计数[MySQL]?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!