DQL語言及用法
DQL(Data Query Language) 數據查詢語言,主要是對數據表進行查詢操作,用到的動詞主要有Select、Where、Order By(Desc Asc)、Group By、Limit。
案例用表創建鏈接:https://blog.csdn.net/Mr_VanGogha/article/details/106973108
常用動詞介紹
動詞 | 作用 |
---|---|
Select | 查詢動詞 |
Where 條件 | 對條件進行判斷 |
Order By | 排序,其中Desc爲升序,Asc爲降序 |
Group By | 分組 |
Limit start len | 第一個返回記錄行的偏移量,第二個參數指定返回記錄行的最大數目 |
基本語法
1.查詢所有的學生
Select * from student;
2.查詢學號爲001的學生信息(Where)
Select * from student where stuNo = '001';
3.通過學號遞減展示所有學生信息(Order By ,Asc爲遞增,Desc爲遞減)
Select * from student Order By stuNo Desc;
4.通過性別進行分組(Group By)
Select gender,count(*) as '數量' from student Group By gender;
5.查詢性別爲男的學生數量
1.Select gender,count(*) as '數量' from student Group By gender having gender = '男';
2.Select gender,count(*) as '數量' from student where gender = '男' Group By gender;