MySQL - 返回匹配查询数据的行数？

Question

我有一个查询，如下所示：

SELECT 1 FROM shop_inventory a JOIN shop_items b ON b.id=a.iid AND b.szbid=3362169 AND b.cid=a.cid WHERE a.cid=1 GROUP BY a.bought 

我需要这方面的数据做的唯一一件事就是制定出返回的行数（我可以用mysqli -> num_rows;做不过，我想知道，如果有返回与查询匹配的行数，而不必运行num_rows的方法？

例如，查询应返回一行，用一个结果，number_of_rows。

我希望这是有道理的！

Answer 1

select count(*) as `number_of_rows` 
from (
    select 1 
    from shop_inventory a 
    join shop_items b on b.id = a.iid 
     and b.szbid = 3362169 
     and b.cid = a.cid 
    where a.cid = 1 
    group by a.bought 
) a 

在这种情况下，由于不使用任何聚合函数和GROUP BY仅仅是消除重复，你也可以这样做：

select count(distinct a.bought) as `number_of_rows` 
from shop_inventory a 
join shop_items b on b.id = a.iid 
    and b.szbid = 3362169 
    and b.cid = a.cid