查询返回的行太少 [英] Query returns too few rows

问题描述

设置:

mysql> create table product_stock(
       product_id integer, qty integer);
Query OK, 0 rows affected (0.17 sec)

mysql> create table product(
       product_id integer, product_name varchar(255));
Query OK, 0 rows affected (0.11 sec)

mysql> insert into product(product_id, product_name) 
       values(1, 'Apsana White DX Pencil');
Query OK, 1 row affected (0.05 sec)

mysql> insert into product(product_id, product_name) 
       values(2, 'Diamond Glass Marking Pencil');
Query OK, 1 row affected (0.03 sec)

mysql> insert into product(product_id, product_name) 
       values(3, 'Apsana Black Pencil');
Query OK, 1 row affected (0.03 sec)

mysql> insert into product_stock(product_id, qty) 
       values(1, 100);
Query OK, 1 row affected (0.03 sec)

我的第一个查询:

mysql> SELECT IFNULL(SUM(s.qty),0) AS stock, 
              product_name 
       FROM product_stock s 
        INNER JOIN product p ON p.product_id=s.product_id 
       GROUP BY product_name 
       ORDER BY product_name; 

返回:

+-------+---------------------------+ 
| stock | product_name              | 
+-------+---------------------------+ 
| 100   | Apsana White DX Pencil    | 
+-------+---------------------------+ 
1 row in set (0.00 sec) 

但是我想得到以下结果:

But I want to have the following result:

+-------+------------------------------+ 
| stock | product_name                 | 
+-------+------------------------------+ 
|   0   | Apsana Black Pencil          | 
| 100   | Apsana White DX Pencil       | 
|   0   | Diamond Glass Marking Pencil | 
+-------+------------------------------+ 

要获得此结果，我应该运行什么mysql查询?

To get this result what mysql query should I run?

推荐答案

您需要翻转联接并使用LEFT JOIN代替INNER JOIN:

You need to flip your join around and use LEFT JOIN instead of INNER JOIN:

SELECT IFNULL(SUM(s.qty),0) AS stock, product_name
FROM product AS p
LEFT JOIN product_stock AS s ON p.product_id=s.product_id
GROUP BY product_name
ORDER BY product_name;

这篇关于查询返回的行太少的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！