Question

我正在为订单开发一个赋值函数，我正在尝试将订单分配给具有最少待处理请求的用户。我想获取用户ID，其中pending的值是所有用户中最少的。

示例：

userID    pending
------    -------
0         3
1         0 <----This user has the least pending of all
2         4

如何设置SQL查询以返回表中待处理请求数最少的用户ID？

$sql="SELECT user_id FROM writerdata_tb WHERE pending = '//Minimum pending here//' LIMIT 1";
$assign = $conn->query($sql);
$row = $assign->fetch_assoc();

Answer 1

对所提出的各种可能答案的比较：

EXPLAIN SELECT aa.userId, aa.pending
FROM writerdata_tb AS aa
INNER JOIN writerdata_tb AS bb 
ON aa.userId = bb.userId
WHERE aa.pending >= bb.pending
ORDER BY aa.pending ASC
LIMIT 1;

id  select_type     table   type    possible_keys   key     key_len     ref     rows    Extra   
1   SIMPLE  aa  ALL     PRIMARY     NULL    NULL    NULL    4   Using temporary; Using filesort
1   SIMPLE  bb  ALL     PRIMARY     NULL    NULL    NULL    4   Using where; Using join buffer (Block Nested Loop)

EXPLAIN SELECT userId, pending
FROM writerdata_tb
WHERE pending = (
    SELECT MIN(pending)
    FROM writerdata_tb 
);

id  select_type     table   type    possible_keys   key     key_len     ref     rows    Extra   
1   PRIMARY     writerdata_tb   ALL     NULL    NULL    NULL    NULL    4   Using where
2   SUBQUERY    writerdata_tb   ALL     NULL    NULL    NULL    NULL    4   NULL

EXPLAIN SELECT userId, pending
FROM writerdata_tb
ORDER BY pending ASC
LIMIT 1;

id  select_type     table   type    possible_keys   key     key_len     ref     rows    Extra   
1   SIMPLE  writerdata_tb   ALL     NULL    NULL    NULL    NULL    4   Using filesort

EXPLAIN SELECT t.userId
FROM writerdata_tb AS t
GROUP BY (
    t.userId
)
ORDER BY SUM(pending) ASC
LIMIT 1;

id  select_type     table   type    possible_keys   key     key_len     ref     rows    Extra   
1   SIMPLE  t   index   PRIMARY     PRIMARY     4   NULL    4   Using temporary; Using filesort

Answer 2

您可以按列待处理订购结果（请参阅Simone Nigro对查询的评论）。使用 limit 字，在结果中您将只获得第一行，在这种情况下，您将获得minium挂起值的结果。

我现在看到Aleksandar Miladinovic的情况，如果表中有许多行具有相同的值待定：您可以执行：

获取待处理列
使用上一步中获取的值来接收具有该值的行

SELECT user_id FROM writerdata_tb WHERE pending =（SELECT min（pending）FROM writerdata_tb）

Answer 3

尝试这种方式：从writerdata_tb中选择userID，其中pending =（从writerdata_tb中选择min（pending））;

Answer 4

如果重复用户ID

SELECT
    t.userID
from 
    tasks as t
group by (t.userID)
order by sum(pending) asc 
limit 1

否则

SELECT
    t.userID
from 
    tasks as t
order by pending asc 
limit 1

从列中选择一个SQL值，其中单独的列为MIN（）

4 个答案: