Question

我是sql的新手，并且已经设法通过下面的sql选择与许多表相关的行。我现在有一张第四张桌子，上面列出了该模型的“子项”。模型表中的“ id”（526行）和项目表中的“ model_id”（1505行）之间存在关联。现在，我要计算项目表中与模型表中的id具有相同的model_id的项目，并将其输出为Items_in_model。

SELECT models.id AS Id, categories.name AS Category, models.category_name 
AS CategoryName, manufacturers.name AS Manufacturer, models.model AS Model, 
models.day_price AS dayprice, models.week_price AS weekprice 
FROM
models, categories, manufacturers
WHERE models.category=categories.id AND 
models.manufacturer=manufacturers.id 
ORDER BY CategoryName ASC

我使用此sql进行计数工作“独立”

SELECT COUNT(items.id) AS Count FROM items WHERE items.model_id 
LIKE 2

我尝试了许多不同的方法，但这是唯一没有给我错误但只输出一行（共526个）并且计数为（所有项目均为1505个）的方法

SELECT models.id AS Id, categories.name AS Category, 
models.category_name AS CategoryName, COUNT(items.id) AS Count, 
manufacturers.name AS Manufacturer, models.model AS Model, 
COUNT(DISTINCT(items.id)) AS ModelCount, models.day_price AS dayprice, 
models.week_price AS weekprice 
FROM
models, categories, manufacturers, items
WHERE models.category=categories.id AND 
models.manufacturer=manufacturers.id AND models.id=items.model_id
ORDER BY CategoryName ASC

谢谢！

Answer 1

您的目标不是100％明确，但这是我的猜测：

SELECT m.id AS Id, 
    c.name AS Category,
    m.category_name AS CategoryName,
    manufacturers.name AS Manufacturer,
    m.model AS Model, 
    COUNT(i.id) AS ModelCount,
    m.day_price AS dayprice, 
    m.week_price AS weekprice 
FROM models m
LEFT JOIN categories c
ON m.category=c.id
LEFT JOIN manufacturers
ON m.manufacturer=manufacturers.id
LEFT JOIN items i
ON m.id=i.model_id
GROUP BY  m.id

更新不确定您的新问题，但是我怀疑您需要额外的JOIN。尝试这种方式：

SELECT m.id AS Id, 
    c.name AS Category,
    m.category_name AS CategoryName,
    manufacturers.name AS Manufacturer,
    m.model AS Model, 
    COUNT(i.id) AS ModelCount,
    SUM(IF(i.reservable = 1,1,0)) AS ModelReservableCount,
    m.day_price AS dayprice, 
    m.week_price AS weekprice 
FROM models m
LEFT JOIN categories c
ON m.category=c.id
LEFT JOIN manufacturers
ON m.manufacturer=manufacturers.id
LEFT JOIN items i
ON m.id=i.model_id
GROUP BY  m.id

在mysql中使用关系时如何获取行数

1 个答案: