如何使用MySQL中的最后一行值来计算出现次数

Question

I've written the following query to get the number of times the code field equals the last code field. At the same time, I am a complete newbie to this type of syntax (Using Variables) in MySQL.

    select
          @lastCode:= ts.code as lastCode,
    @count:= 0 as count,
          ts.id,
          ts.date,
          ts.code, 
if( @lastShiftCode = ts.shift_code, @count := @count + 1,  @count:= 0) as occurences 

       from
          empCodes ts
       WHERE
       ts.date between '2018-01-01' and '2018-02-01' 
       order by
          ts.id,
          ts.date

The query runs, but the count never changes from 0 and neither the occurrences changes from 1. I would expect the occurrences to go up by one each row.

Here is part of the output

lastCode    count   id  date        code occurrences
XX1         0       2   01/02/2018  XX1  1
XX1         0       2   02/02/2018  XX1  1
XX1         0       2   05/02/2018  XX1  1
XX1         0       2   06/02/2018  XX1  1
XX1         0       2   07/02/2018  XX1  1
XX1         0       2   08/02/2018  XX1  1
XX1         0       2   09/02/2018  XX1  1

Answer 1

Try this:

SELECT ts.id, ts.date, SUM(ts.lastCode=ts.code) `count`
FROM empCodes ts
WHERE ts.date BETWEEN STR_TO_DATE('2018-01-01','%Y-%m-%d')
      AND STR_TO_DATE('2018-02-01','%Y-%m-%d') 
GROUP BY  ts.id, ts.date;