MySQL JOIN返回NULL字段

本文介绍了MySQL JOIN返回NULL字段的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我正在尝试在下面运行脚本，但名称字段始终为NULL值.

I'm trying to run script below, but always getting NULL values for name field.

SELECT u.name AS _user_name, s.name AS _school_name FROM fwg_files AS f LEFT JOIN users AS u ON u.id = f.user_id LEFT JOIN user_profiles AS up ON up.user_id = u.id LEFT JOIN school AS s ON s.id = up.profile_value

在我看来，JOIN ON学校表中的问题是，我尝试选择s.id，它也返回NULL值.

The problem seems to me in JOIN ON school table, I tried to SELECT s.id and it returns NULL values also.

表fwg_files

Table fwg_files

id | user_id 240 | 414 241 | 436

表格用户

id | name 414 | Name 1 436 | Name 2

表user_profiles

Table user_profiles

user_id | profile_value 414 | "6" 436 | "14"

餐桌学校

id | name 6 | School 1 14 | School 2

谢谢

推荐答案

不确定数据和架构，但是如果up.profile_value类似于"123"，则可以尝试以下方法:

Not sure about your data and the Schema, but if up.profile_value is like "123", you can try this:

SELECT u.name AS _user_name, s.name AS _school_name FROM fwg_files AS f LEFT JOIN users AS u ON u.id = f.user_id LEFT JOIN user_profiles AS up ON up.user_id = u.id LEFT JOIN school AS s ON CONCAT('"', s.id, '"') = up.profile_value