UC知道请教个SQL问题
来源：百度知道 编辑：UC知道 时间：2024/05/26 14:50:18
select * from test_1 inner join (select min(id) as id from test_1 group by name1 order by id ) T on test_1.id = T.id
select * from test_1 ,(select min(id) as id from test_1 group by name1 order by id ) where test_1.id = T.id
这两个SQL语句怎么理解？涉及到哪些语法？
select * from test_1 ,(select min(id) as id from test_1 group by name1 order by id ) where test_1.id = T.id
这两个SQL语句怎么理解？涉及到哪些语法？
1.全联接：inner join，min:取最小函数，排序嘛
2.和上一句比少个全联接。
其实这2句，如果是小型数据效率都差不多··大型的呢·在id上建立索引，就用第2句就好了··