order by rand()优化
优化前：
SELECT
id,
loan_id,
NAME,
company
FROM
tablename
WHERE
time BETWEEN 1522512000
AND 1525103999
AND loan_time BETWEEN 1522512000
AND 1525103999
AND STATUS = 1
AND is_again_yd = 0
AND company <> 1
order by rand()
LIMIT 30
优化方案一：
采用JOIN，查询max(id) * rand()来随机获取数据。
SELECT
t1.id,
t1.loan_id,
t1. NAME,
t1.company
FROM
`tablename` AS t1
JOIN (
SELECT
ROUND(
RAND() * (
SELECT
MAX(id)
FROM
`tablename`
)
) AS id
) AS t2
WHERE
t1.id >= t2.id
AND time BETWEEN 1522512000
AND 1525103999
AND loan_time BETWEEN 1522512000
AND 1525103999
AND STATUS = 1
AND is_again_yd = 0
AND company <> 1
ORDER BY t1.id ASC
LIMIT 30;
优化方案二：
1 SELECT 2 t1.id, 3 t1.loan_id, 4 t1.NAME 5 FROM 6 tablename t1 7 WHERE 8 t1.id >= ( 9 SELECT 10 floor( 11 RAND() * ( 12 SELECT 13 MAX(id) 14 FROM 15 `tablename` 16 ) 17 ) 18 ) 19 AND t1.time BETWEEN 1522512000 AND 1525103999 20 AND t1.STATUS IN (1, 2, 4) 21 AND t1.type IN (1, 2) 22 AND t1.belong_company = 0 23 AND t1.is_del = 0 24 AND NOT EXISTS ( 25 SELECT 26 loan_id 27 FROM 28 tablename2 t2 29 WHERE 30 t2.loan_id = t1.loan_id 31 AND t2.company = 1 32 ) 33 ORDER BY id 34 limit 20
说明：这种方案替代mysql rand(),性能太幅度提升，随机性没有rand()强，如果随机性强的请选择替代方案。
