[英]Select a maximum of 2 rows where a column has the same value
我试图选择最多2行,其中一列具有相同的值。 即:
id title accountid date
1 job 1 1 Oct. 1
2 job 2 1 Oct. 1
3 job 3 1 Oct. 1
4 job 1 2 Oct. 2
5 job a 3 Oct. 2
6 job z 4 Oct. 3
7 job 2 2 Oct. 3
8 job 3 2 Oct. 8
我要选择
1 job 1 1 Oct. 1
2 job 2 1 Oct. 1
<----- Skip this row because we already
have 2 from account 1
4 job 1 2 Oct. 2
5 job a 3 Oct. 2
6 job z 4 Oct. 3
7 job 2 2 Oct. 3
我现在用来选择的是这样的:
SELECT *
FROM table
ORDER BY date DESC, RAND()
我已经考虑过使用HAVING COUNT(accountid) <= 2
但这只会引起混乱。 我对使用sql很新。
谢谢你的帮助!
更新:
您好,感谢您的所有快速回复。 我已经尝试了其中的每一个,但似乎无法使它们正常工作。 我想出了一种方法来限制使用php每个帐户ID的作业。 再次感谢您的时间和努力,以帮助我解决这个问题。
set @id := 0, @acid := 0;
select t.id, title, accountid, `date`
from
t
inner join (
select
id,
if(@acid = accountid, @i := @i + 1, @i := 1) as i,
@acid := accountid as acid
from t
order by accountid, `date` desc
) s on t.id = s.id
where s.i <= 2
您好,这可以解决您的问题,但我不知道此查询的速度如何。
查询:
SELECT
id,
title,
accountid,
date
FROM
(SELECT
IF(@prev != a.accountid, @rownum:=1, @rownum:=@rownum+1) as rownumber,
@prev:=a.accountid,
a.*
FROM (
SELECT
t1.id,
t1.title,
t1.accountid,
t1.date
FROM tbl t1,
(SELECT @rownum := 0, @prev:='') sq
ORDER BY accountid, id) a
)b
WHERE b.rownumber<3
ORDER BY b.id
结果:
| ID | TITLE | ACCOUNTID | DATE |
-----------------------------------
| 1 | job 1 | 1 | Oct. 1 |
| 2 | job 2 | 1 | Oct. 1 |
| 4 | job 1 | 2 | Oct. 2 |
| 5 | job a | 3 | Oct. 2 |
| 6 | job z | 4 | Oct. 3 |
| 7 | job 2 | 2 | Oct. 3 |
SELECT tab.id, tab.title, tab.accountid, tab.date
FROM table tab INNER JOIN table count_tab ON tab.id = count_tab.id
WHERE count_tab.id <= tab.id
GROUP BY tab.id, tab.title, tab.accountid, tab.date
HAVING count(count_tab.id) <= 2
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