mysql - LEFT JOIN 3 个表缺少某些字段 (NULL)

Question

我有一个包含 3 个表的数据库:公司、地址、联系人，其中基本上包含有关公司本身的一些数据及其地址和联系信息。现在，并非所有公司都有地址信息和联系信息。我正在尝试查询数据库以显示所有公司的列表:表格包括公司名称、地址和联系电话。所以我使用这样的查询:

SELECT company.inn, company.name, company.ceo, address.city, contact.phone
    FROM company 
    JOIN address
    JOIN contact
    ON company.id = address.company_id AND company.id = contact.company_id

效果很好，但它不会返回没有地址或联系方式或两者都没有的公司。所以我然后尝试发出左连接命令:

SELECT company.inn, company.name, company.ceo, address.city, contact.phone
    FROM company 
    LEFT JOIN address
    LEFT JOIN contact
    ON company.id = address.company_id AND company.id = contact.company_id

我得到这个错误:

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '' at line 1

Answer 1

SELECT company.inn, company.name, company.ceo, address.city, contact.phone
FROM company 
LEFT JOIN address
ON company.id = address.company_id
LEFT JOIN contact 
ON company.id = contact.company_id

ON 必须在 JOIN 之后定义。您可以在此处阅读文档 https://dev.mysql.com/doc/en/join.html