更新时间:2022-11-30 18:15:22
这有效:
SELECT c.id, COUNT(f.name) FROM color c LEFT JOIN fruit f ON c.id = f.color_id GROUP BY c.id
您必须计算一个水果字段,以便可以返回NULL,该值变为零.
You have to count a field of fruit, so that NULL can be returned, which becomes a zero.
使用LEFT JOIN和GROUP BY的COUNT(*)在MySQL中包括NULL
MYSQL:COUNT与GROUP BY,LEFT JOIN和WHERE子句不返回零值
使用多个LEFT JOIN和GROUP BY优化MySQL查询