使用join计算sql中的一个字段

Question

我有一个名为rendeles_termekek的表。（英文，ordered_products）

我想算一下，每件产品的订购次数。

使用下面的SQL，我得到4作为ennyi。我上传了一张图片，并为每行写了正确的数字。

SELECT DISTINCT

                    rendeles_termekek.termek_id,
                    termek.termek_id, 
                    termek.termek_nev,

                    ( SELECT COUNT(rendeles_termekek.termek_id) FROM rendeles_termekek ) AS ennyi

                FROM rendeles_termekek

                LEFT JOIN termek ON rendeles_termekek.termek_id = termek.termek_id

                ORDER BY termek.termek_nev ASC

Answer 1

我认为你的表中只有四行＆＃34; rendeles_termekek＆＃34;。

我已更新您的查询。试试这个

SELECT DISTINCT
                rendeles_termekek.termek_id,
                termek.termek_id, 
                termek.termek_nev,
                ( SELECT COUNT(rendeles_termekek.termek_id) FROM rendeles_termekek r where r.termek_id = r1.termek_id ) AS ennyi
            FROM rendeles_termekek r1
            LEFT JOIN termek ON rendeles_termekek.termek_id = termek.termek_id
            ORDER BY termek.termek_nev ASC

请注意，我更改了子查询并在其中添加了where条件

   `( SELECT COUNT(rendeles_termekek.termek_id) FROM rendeles_termekek r where r.termek_id = r1.termek_id ) AS ennyi`

Answer 2

**r1** is the alias of your table rendeles_termekek so you have to access those columns through alias name "r1" like I did in below query. try below

SELECT DISTINCT
                r1.termek_id,
                termek.termek_id, 
                termek.termek_nev,
                ( SELECT COUNT(r.termek_id) FROM rendeles_termekek r where r.termek_id = r1.termek_id ) AS ennyi
            FROM rendeles_termekek r1
            LEFT JOIN termek ON r1.termek_id = termek.termek_id
            ORDER BY termek.termek_nev ASC