MySQL Join AND EXISTS 组合

Question

个案我收到以下查询：

SELECT * FROM `parking_parking`
JOIN `parking_address` ON `parking_parking`.`parking_address` = `parking_address`.`address_id`
WHERE `parking_id` = 3

此查询选择有关停车场的信息（有关停车场本身的地址和数据）

总的来说..它有效！

问题

虽然有一个小问题.. 每当地址已从数据库中删除并且停车场本身仍然存在时。整个查询 returns 0。只是因为它查找和 A AND B 链接。但是，如果找不到一个，第二个也不会返回。

现在有解决办法了.. 存在

但是我不知道怎么用

我试过了：

EXISTS JOIN 

JOIN EXISTS 

JOIN `parking_address` ON EXISTS

但是没有用。

我希望（并猜测）我忽略了一件小事。

Note

!! I do not use this in real life! !!
SELECT * FROM
I did this one when I was still at the veeeery basics and I found out the hard way that even the simplest pages took ages to load.

解决方案：GolezTrol

SELECT * FROM `parking_parking`
LEFT JOIN `parking_address` ON `parking_parking`.`parking_address` = `parking_address`.`address_id`
WHERE `parking_id` = 3

Answer 1

将join（inner join的缩写）改为left join（=left outer join）。这将 return 所有 parkings，如果没有匹配的 address[=20]，地址字段将 return null =]:

SELECT * FROM `parking_parking` LEFT JOIN `parking_address` ON `parking_parking`.`parking_address` = `parking_address`.`address_id` WHERE `parking_id` = 3

MySQL Join AND EXISTS 组合

MySQL Join AND EXISTS in combination

mysql

join

exists