表名：t_student
查询表数据内容（显示位置做了切换以及筛选）
SELECTid,stuName,age,sex,gradeName FROM t_student ;
SELECTstuName,id,age,sex,gradeName FROM t_student ;
SELECT * FROMt_student;
SELECTstuName,gradeName FROM t_student;
指定查询主键id=1的行
SELECT * FROMt_student WHERE id=1;
指定查询age数据大于22的行
SELECT * FROMt_student WHERE age>22;
指定查询age数据大于21和23的单行
SELECT * FROMt_student WHERE age IN (21,23);
指定查询age数据21到23之外的单行
SELECT * FROMt_student WHERE age NOT IN (21,23);
指定查询21到24之内的全部行数
SELECT * FROMt_student WHERE age BETWEEN 21 AND 24;
指定查询21到24之外的全部行数
SELECT * FROMt_student WHERE age NOT BETWEEN 21 AND 24;
模糊查询：%表示多个任意字符 _表示单个任意字符
SELECT * FROMt_student WHERE stuName LIKE '张三';
SELECT * FROMt_student WHERE stuName LIKE '张三%';
SELECT * FROMt_student WHERE stuName LIKE '张三__';
SELECT * FROMt_student WHERE stuName LIKE '%张三%';
查询字符串为null的数据
SELECT * FROMt_student WHERE sex IS NULL;
查询字符串不是为null的数据
SELECT * FROMt_student WHERE sex IS NOT NULL;
查询表中一年级并且是23岁的
SELECT * FROMt_student WHERE gradeName='一年级' AND age=23
查询表中一年级和23岁的
SELECT * FROMt_student WHERE gradeName='一年级' OR age=23
列出所有grandeName列的数据
SELECT DISTINCTgradeName FROM t_student;
列出所有grandeName列的数据升序和降序
SELECT * FROMt_student ORDER BY age ASC;
SELECT * FROMt_student ORDER BY age DESC;
group用法重点：
将gradeName为主列GROUP_CONCAT(stuName)为从列，查询gradeName中有多少个stuName并且以逗号隔开显示
SELECTgradeName,GROUP_CONCAT(stuName) FROM t_student GROUP BY gradeName;
将gradeName为主列GROUP_CONCAT(stuName)为从列，查询gradeName数量是多少
SELECT gradeName,COUNT(stuName)FROM t_student GROUP BY gradeName;
将gradeName为主列GROUP_CONCAT(stuName)为从列，查询gradeName中有3次以上的stuName列的数据
SELECT gradeName,COUNT(stuName) FROM t_student GROUP BY gradeName HAVING COUNT(stuName)>3;
将gradeName为主列GROUP_CONCAT(stuName)为从列，统计stuName总数
SELECTgradeName,COUNT(stuName) FROM t_student GROUP BY gradeName WITH ROLLUP;
将gradeName为主列GROUP_CONCAT(stuName)为从列，统计stuName总数以逗号形式分开显示
SELECTgradeName,GROUP_CONCAT(stuName) FROM t_student GROUP BY gradeName WITH ROLLUP;
分页查询
0代表第一行数据 0,5 代表显示第一行数据到第五行数据为一页
SELECT * FROMt_student LIMIT 0,5;
SELECT * FROMt_student LIMIT 5,5;
SELECT * FROMt_student LIMIT 10,5;