php - 多表 JOIN 抛出 'Not unique table/alias' 错误

Question

以下查询会引发错误:

SELECT * FROM proposal_data
  INNER JOIN proposal_data
      ON proposal_data_second.proposal_id = proposal_data.proposal_id

  INNER JOIN proposal_data_second   
      ON proposal_data_third.proposal_id =  proposal_data_second.proposal_id
  INNER JOIN proposal_data_third
      ON proposal_data_fourth.proposal_id = proposal_data_third.proposal_id

错误是:

#1066 - Not unique table/alias: 'proposal_data'

我做错了什么？

Answer 1

您错误地连接了表。

在当前查询中，您在声明之前连接表:

例如取前三行

SELECT * FROM proposal_data
  INNER JOIN proposal_data
      ON proposal_data_second.proposal_id = proposal_data.proposal_id

在声明 proposal_data_second 表之前，您需要将 proposal_data 与 proposal_data_second 连接起来。

此外，您不需要使用表名 peoposal_data 两次:

SELECT * FROM proposal_data
  INNER JOIN proposal_data --This is invalid syntax

试试这个:

SELECT * FROM proposal_data
   INNER JOIN proposal_data_second
           ON proposal_data_second.proposal_id = proposal_data.proposal_id
   INNER JOIN proposal_data_third
           ON proposal_data_third.proposal_id = proposal_data_second.proposal_id
   INNER JOIN proposal_data_fourth
           ON proposal_data_fourth.proposal_id = proposal_data_third.proposal_id

更多信息请参见MySQL: JOIN Syntax