mysql - 为什么我的 JOIN 显示双重结果？

Question

这就是我的查询的样子，但它产生了双重结果。我是 SQL 的新手。

SELECT * FROM tbl_projects p, tbl_issues i WHERE p.admin_id = 3 

Answer 1

您正在以旧方式加入，没有加入条件，所以您得到笛卡尔积。请使用明确的 join 语法:

SELECT   * -- It is recommended to explicitly select the attributes you need
FROM     tbl_projects p
JOIN     tbl_issues i -- I assumed inner join
      ON p.id = i.project_id -- You'll have to figure out the conditions yourself
WHERE    p.admin_id = 3