Question

我正在努力优化查询

（从1个表中选择2个随机用户）

id  | name |  total | img
------------------------ --
1    user1   500      1
2    user2   600      2
3    user3   650      3

需要结果和ABS（total1 -total2）＆lt; 200

id1  | id2|  name1 | name2 | img1 | img2 |  total1 | total2
------------------------ -------------------------------------
1       3    user1   user3    1      3        500      650

获得更多性能重写：

SELECT
  C1.id AS id1, C1.img AS img1, C1.name AS name1,
  C2.id AS id2, C2.img AS img2, C2.name AS name2,
  C1.total AS total1, C2.total AS total2
FROM users C1, users C2
WHERE C1.id <> C2.id 
  AND ABS(C1.total - C2.total) < 200
ORDER BY RAND()
LIMIT 1

要

$dbh = new PDO ("mysql:host=$hostname;dbname=$dbname","$username","$pw");
$rs = $dbh->query(
"SELECT COUNT(*) AS 'count'
 FROM users C1, users C2
 WHERE C1.id <> C2.id
   AND ABS(C1.total - C2.total) < 200");
$target = rand(0,$rs[0]['count']);
$rs = $dbh->query(
  "SELECT 
   C1.id AS id1, C1.img AS img1, C1.name AS name1,
   C2.id AS id2, C2.img AS img2, C2.name AS name2,
   C1.total AS total1, C2.total AS total2
  FROM users C1, users C2
  WHERE C1.id <> C2.id
   AND ABS(C1.total - C2.total) < 200
  LIMIT ?,1",
array($target));


foreach ($rs as $row) 
                    { 
                     print $row['name1']; 
                     }

返回empry结果，我错过了，与db的连接是正常的（另一个查询正在运行）

Answer 1

要选择两个随机记录，我通常会做一个

// Whatever your query is
order by rand() 
limit 2

然后你可以从这两个随机记录中做出你需要的任何计算。

Answer 2

以下是您的解决方案：

SELECT u1.id1, u2.id2, u1.name1, u2.name2, u1.total1, u2.total2, u1.img1, u2.img2 
FROM 
(
    SELECT u.id id1, u.name name1, u.total total1, u.img img1 
    FROM users u 
    ORDER BY RAND()
) u1
CROSS JOIN
(
    SELECT u.id id2, u.name name2, u.total total2, u.img img2 
    FROM users u 
    ORDER BY RAND()
) u2
WHERE u1.id1 != u2.id2 AND ABS(u1.total1 - u2.total2) < 200
LIMIT 0,1;

Demo

Answer 3

尝试使用prepare()和execute()：

$stmt = $dbh->prepare(
  "SELECT 
   C1.id AS id1, C1.img AS img1, C1.name AS name1,
   C2.id AS id2, C2.img AS img2, C2.name AS name2,
   C1.total AS total1, C2.total AS total2
  FROM users C1, users C2
  WHERE C1.id <> C2.id
   AND ABS(C1.total - C2.total) < 200
  LIMIT ?,1");
$stmt->execute(array($target));

$rs = $stmt->fetchAll();

单个查询而不是两个查询：减少rand()次计算

SELECT C1.id AS id1,
       C1.img AS img1,
       C1.name AS name1,
       C2.id AS id2,
       C2.img AS img2,
       C2.name AS name2,
       C1.total AS total1,
       C2.total AS total2
  FROM(select *, rand() randval from users) C1, users C2
  WHERE C1.id <> C2.id AND ABS(C1.total - C2.total) < 200
  ORDER BY C1.randval DESC
  LIMIT 1;

从一行中选择MySQL中的随机用户

3 个答案: