Question

SELECT 
    COUNT(a)/COUNT(s)*100 as aratio, 
    COUNT(b)/COUNT(s)*100 as bratio, 
    COUNT(c)/COUNT(s)*100 as cratio, 
    COUNT(a), 
    COUNT(b), 
    COUNT(c), 
    COUNT(s) 
FROM 
    (SELECT COUNT(cid) as a FROM images WHERE width > height AND category_id = 4 GROUP BY cid) as aq, 
    (SELECT COUNT(cid) as b FROM images WHERE width < height AND category_id = 4 GROUP BY cid) as bq, 
    (SELECT COUNT(cid) as c FROM images WHERE width = height AND category_id = 4 GROUP BY cid) as cq, 
    (SELECT COUNT(cid) as s FROM images WHERE category_id = 4 GROUP BY cid) as sq;

如何才能使此请求更有效？

Answer 1

可以使用WITH。将所有查询移至WITH并稍加修改：将COUNT(cid)更改为COUNT(DISTINCT cid)并删除GROUP BY条款。

Answer 2

您可以使用以下内容：

SELECT 
    SUM(CASE (width > height) WHEN true THEN 1 ELSE 0 END)::float8*100/COUNT(*) as aratio, 
    SUM(CASE (width < height) WHEN true THEN 1 ELSE 0 END)::float8*100/COUNT(*) as bratio, 
    SUM(CASE (width = height) WHEN true THEN 1 ELSE 0 END)::float8*100/COUNT(*) as cratio, 
    SUM(CASE (width > height) WHEN true THEN 1 ELSE 0 END), 
    SUM(CASE (width < height) WHEN true THEN 1 ELSE 0 END), 
    SUM(CASE (width = height) WHEN true THEN 1 ELSE 0 END), 
    COUNT(*) 
FROM 
    images WHERE category_id = 4;

此查询不按cid分组，但可能您不需要它。

PSQL请求太慢了。怎么解决？

2 个答案: