在连接表中找到的MySQL一对多按订单排序

Question

两张桌子：

table_a
-------
table_a_id: (primary, int)

table_b
-------
table_a_id: (index, int, from table_a)
table_b_value: (varchar)

table_a_id和table_b_value之间的一对多关系。

给出这样的查询：

SELECT DISTINCT(table_a_id) FROM table_a 
JOIN table_b ON table_a.table_a_id=table_b.table_a_id

我想按table_b中table_a_id的出现次数排序。我真的不确定如何在MySQL中写这个。

Answer 1

SELECT COUNT(table_b.table_a_id) AS count 
FROM table_a 
JOIN table_b ON table_b.table_a_id = table_a.id 
GROUP BY table_b.table_a_id 
ORDER_BY count DESC 

Answer 2

选择             a.table_a_id，             COUNT（b.table_a_id）AS a_count     FROM table_a AS a     LEFT JOIN table_b AS b         ON a.table_a_id = b.table_a_id     GROUP BY a.table_a_id     ORDER BY a_count

Answer 3

在这种情况下，为什么你需要加入表格呢？

SELECT table_a_id FROM table_b GROUP BY table_a_id order by count(table_a_id) desc

Answer 4

使用您的示例

SELECT table_a_id, COUNT(*)
FROM table_b
GROUP BY table_a_id

一个真实世界的例子

如果你想要一个像这样的表：

post_id  comments_count
1        20
2        125
3        43

如果您可能需要A表中的其他信息，您可以：

select p.id, count(c.*) comments_count
from posts p
join comments c on c.post_id = p.id
group by p.id

如果您不需要A表中的任何内容，则可以简化：

select post_id, count(*)
from comments
group by post_id