mysql - 加入 3 个表，其中 2 个是 SELECT *

Question

我正在通过重新测试进行研究。我有三张桌子。一张表用于 Demographics，我只需要从中获取有限数量的数据。其他两个表各有 235 个字段，唯一的区别是表名。我试过这样的陈述：

SELECT * FROM research_statement_answers, statement_answers, demographic_answers
WHERE (( research_statement_answers.id_Questions = demographic_answers.id_Demographic)
and (statement_answers.id_Questions = demographic_answers.id_Demographic)
and (demographic_answers.Research_Completed = 1))

但这不起作用。我见过的所有示例都要求我命名两个表中的所有 235 个字段。我可以做到，但我不敢相信这是最好的方法。因此，建议最受欢迎。谢谢你。瑞克

Answer 1

SELECT
    research_statement_answers.*,
    statement_answers.*,
    demographic_answers.*
FROM ...

由于这些表仅在名称上有所不同，在它们上使用 UNION JOIN 不是更好吗？

结果将是您拥有所有表记录的重聚。

使用普通连接，结果是每条记录有 235*3 列，记录的子集表示三个表之间的交集。

Answer 2

您可以通过执行以下操作从多个表中选择 * 并仅包含第三个表的特定列：

SELECT
    research_statement_answers.*,
    statement_answers.*,
    demographic_answers.id,
    demographic_answers.title,
    demographic_answers.etc
FROM ...

Answer 3

    SELECT 
    research_statement_answers.*, 
    statement_answers.*,
    demographic_answers.*
 FROM research_statement_answers
    JOIN demographic_answers ON demographic_answers.id_Demographic = research_statement_answers.id_Questions
    JOIN statement_answers ON demographic_answers.id_Demographic = statement_answers.id_Questions
    WHERE demographic_answers.Research_Completed = 1