LEFT JOIN 返回所有空值

Question

所以我的查询返回了正确数量的结果，但由于某种原因，左连接结果都是 NULL 值。这是查询：

SELECT invoices.* FROM appointments
LEFT JOIN invoices ON 'appointments.invoice_guid' = 'invoices.guid'

结果

guid       created_at      status
NULL       NULL            NULL
NULL       NULL            NULL

表格

invoices
    - guid
    - created_at
    - status

appointments
    - guid
    - created_at
    - status
    - invoice_guid

Answer 1

您使用的引号有误，请将其删除

SELECT invoices.* 
FROM appointments
LEFT JOIN invoices ON appointments.invoice_guid = invoices.guid

您使用它们的方式是比较两个字符串，它们是不同的，所以您不加入任何东西

Answer 2

去掉单引号 'appointments.invoice_guid' = 'invoices.guid'

LEFT JOIN returning all null values