mysql - 如何计算表中每一行的行数？

Question

我从table1获取行:

SELECT table1.id,  COUNT(commentTable1.id) AS CNT3,  COUNT(photoTable1.id) AS CNT2, COUNT(fileTable1.id)  AS CNT3 FROM table1 
LEFT JOIN commentTable1 ON...
LEFT JOIN photoTable1 ON...
LEFT JOIN fileTable1 ON ...

如何正确地对每个 COUNT 使用 GROUP BY ？现在我得到了错误的 CNT3

数量

Answer 1

您无法按计数分组，因此我假设您按 table1.id 分组

SELECT table1.id,  COUNT(commentTable1.id) AS CNT3,  COUNT(photoTable1.id) AS CNT2, COUNT(fileTable1.id)  AS CNT3 FROM table1 
LEFT JOIN commentTable1 ON...
LEFT JOIN photoTable1 ON...
LEFT JOIN fileTable1 ON ...
GROUP BY table1.id