如何对后续行进行分组(基于标准)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

假设我有一个这样的表(按日期排序):

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

我想对具有相同名称"值的后续行进行分组并对其进行计数:

I want to group subsequent rows that have the same 'name' value and count them:

name | count 
A    | 2
B    | 1
A    | 3

我正在考虑编写一个存储过程并使用游标，但我也想知道是否有更简单的解决方案，例如使用嵌套的 SELECT 等.

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.

我的问题非常类似于:如何对数组进行分组和计数，但那个是关于 PHP 的.

My question is very similar to: how to group array and count them, but that one concerns PHP.

推荐答案

为此我使用了几个变量，表结构，我创建自己的只是为了测试，它是:

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  )

查询结束是这样的:

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

您可以在 SQLFIDDLE 中看到它的工作原理，如果您有任何问题，请告诉我知道.

you can see it works in SQLFIDDLE if you have any question let me know.

在 SQLFIDDLE 中

In the SQLFIDDLE

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