問題描述

比如這條語句可以統(tǒng)計(jì)查詢總數(shù)

SELECT COUNT(`id`) AS `num` FROM `test`;

那如果加了一句group by 之后就不對(duì)了

SELECT COUNT(`id`) AS `num` FROM `test` GROUP BY `id`;

請(qǐng)問我想要知道GROUP BY出來有多少行數(shù)據(jù)，怎么做

問題解答

統(tǒng)計(jì)GROUP BY后的數(shù)據(jù)行數(shù)：

SELECT count(1) FROM ( SELECT * FROM `test` GROUP BY `id`) AS tmp;

統(tǒng)計(jì)id相同出現(xiàn)的次數(shù)：

SELECT id, count(1) FROM `test` GROUP BY `id`;

統(tǒng)計(jì)GROUP BY后的數(shù)據(jù)總和：

SELECT sum(c) FROM ( SELECT count(1) AS c FROM `test` GROUP BY `id`) AS tmp;

不清楚你想要查什么，但猜測(cè)是第一條SQL。

SELECT id,COUNT(id) AS num FROM test GROUP BY id;

樓主正解，思路就是先把查找到的結(jié)果放在一張“臨時(shí)表”，然后再統(tǒng)計(jì)總數(shù)

樓上正解，題主可參考