与LEFT JOINS的DISTINCT

Question

我从不同的表中获取记录并避免重复行我使用GROUP BY子句，DISTINCT比GROUP BY快，所以我尝试了大量JOIN查询DISTINCT（作为GROUP BY的替代）但它也会获取重复记录。任何想法我怎样才能实现优化，最快和最优有效的查询。

查询示例：

此处索引在项目表的projectId字段中设置。

SELECT DISTINCT p.*, p.projectId as proId, plat.*, con.*, dom.*, sta.*, tech.*, role.*, pimg.*, c.*, dur.* 
                FROM projects p 
                LEFT JOIN projectplatforms pplat ON p.projectId = pplat.projectId JOIN platforms plat ON plat.platformId = pplat.platformId 
                LEFT JOIN projectcountries pcon ON p.projectId = pcon.projectId JOIN countries con ON con.countryId = pcon.countryId 
                LEFT JOIN projectdomains pdom ON p.projectId = pdom.projectId JOIN domains dom ON dom.domainId = pdom.domainId 
                LEFT JOIN statuses sta ON p.statusId = sta.statusId 
                LEFT JOIN projecttechs ptech ON p.projectId = ptech.projectId JOIN technologies tech ON tech.techId = ptech.techId 
                LEFT JOIN projectroles prole ON p.projectId = prole.projectId JOIN roles role ON role.roleId = prole.roleId 
                LEFT JOIN projectimages pimg ON p.projectId = pimg.projectId
                LEFT JOIN clients c ON p.clientId = c.clientId 
                LEFT JOIN durations dur ON p.durationId = dur.durationId 
                WHERE p.featured = 1 
                ORDER BY p.year DESC

Answer 1

使用DISTINCT mysql将返回所有唯一行。如果您在列的一个或部分列表上使用GROUP BY，则不一样。您可能想要使用GROUP BY而不是DISTINCT。