Question

我有两个表products(id, name)和products_cost(id, sid, cost)。

我正在尝试获取总成本低于1000的产品清单，包括没有成本的产品。

我已经尝试过了：

SELECT a.name, SUM(b.cost) AS price
FROM products a
LEFT JOIN products_cost b
ON a.id = b.sid
GROUP BY a.name
HAVING SUM(b.cost)<1000;

上面的SQL仅给出了包含成本的产品名称列表，我希望输出列表中也包含不包含成本的产品名称。

Answer 1

我认为您需要检查null子句中的having值：

SELECT p.name, SUM(pc.cost) AS price
FROM products p LEFT JOIN
     products_cost pc
     ON p.id = b.sid
GROUP BY p.name
HAVING SUM(pc.cost) < 1000 OR SUM(pc.cost) IS NULL;

请注意，我也固定了逻辑（salary在SUM()中没有意义）。我介绍了有意义的表别名-表名的缩写。

Answer 2

使用子查询并加入

   select p.*,a.s as cost from product p left join (
     select pid,sum(cost) as s
     from products_cost
    group by pid
    having s<1000 ) a on p.id=a.pid

Answer 3

您还可以在IFNULL子句中添加HAVING表达式

SELECT a.name, SUM(b.cost) AS price
FROM products a
LEFT JOIN products_cost b
ON a.id = b.sid
GROUP BY a.name
HAVING SUM(IFNULL,b.cost,0)<1000;

左连接问题，使用具有带有和的子句

3 个答案: