应该如何编写将多行合并为单行的 MySQL 语句？

Question

I have multiple rows in MySQL table the follow:

| time       | status | count  | size   |
+------------+--------+--------+--------+
| 2017/01/22 |     -1 | 111111 | NULL   | 
| 2017/01/22 |      0 | 555555 | NULL   |
| 2017/01/22 |      1 | 333333 | 123456 |
| 2017/01/21 |      0 | 666666 | NULL   |
| 2017/01/21 |      1 | 444444 | 234567 |

Now I want to get the follow content:

| time       | total  | success | failed | buffer |
+------------+--------+---------+--------+--------+
| 2017/01/22 | 555555 |  333333 | 111111 | 123456 |
| 2017/01/21 | 666666 |  444444 |      0 | 234567 |

I use time as id , total is count when status=0 , success is count when status=1 , failed is count when status=-1 , buffer is size when status=1 .

So should I how write MySQL statement?

Answer 1

You could use a self join

select a.time, a.count as totale, b.count  as success, c.count as failed, b.size as buffer 
from my_table as a 
left join my_table as  b on a.time = b.time and b.status = 1
left join my_table as  c on a.time = c.time and b.status = -1
where a.status = 0

Answer 2

You need to use sub-queries in order to get the data on the same line. Each sub-query searches for a specific type of data then an outer query joins the data together based on their times. This should do what you are looking for:

SELECT success.time, success.count AS success, failed.count AS failed, buffered.count AS buffered
FROM (
(SELECT `count`, `time`
FROM tbl
WHERE `status` = 0) AS success
INNER JOIN 
    (SELECT `count` `time`
    FROM tbl
    WHERE `status` = 1) AS failed ON failed.time = success.time
INNER JOIN 
    (SELECT `count` `time`
    FROM tbl
    WHERE `status` = -1) AS buffered ON buffered.time = success.time
)