SQL数据查询

Posted 2020-11-02 韩凯

CREATE TABLE class0328(
    id INT,
    cname VARCHAR(10),
    sex VARCHAR(5),
    age INT,
    birthday DATE,
    html DOUBLE,
    js DOUBLE,
    score DOUBLE
)
DESC class0328;
DROP TABLE class0328;
INSERT INTO class0328 VALUES(1,‘董斌‘,‘男‘,25,‘1993-09-13‘,80,10,60);
INSERT INTO class0328 VALUES(2,‘张锐‘,‘男‘,25,‘1993-09-25‘,81,50,60);
INSERT INTO class0328 VALUES(3,‘王荣臣‘,‘男‘,23,‘1996-07-07‘,30,55,65);
INSERT INTO class0328 VALUES(4,‘韩凯‘,‘男‘,26,‘1991-05-20‘,25,52,80);
INSERT INTO class0328 VALUES(5,‘张禄‘,‘男‘,26,‘1991-03-02‘,60,54,80);
INSERT INTO class0328 VALUES(6,‘刘继勋‘,‘男‘,24,‘1994-11-27‘,0.5,20,53);
INSERT INTO class0328 VALUES(7,‘张维‘,‘男‘,29,‘1989-02-24‘,100,50,45);
INSERT INTO class0328 VALUES(8,‘牛攀‘,‘男‘,29,‘1989-12-24‘,100,55,98);
INSERT INTO class0328 VALUES(8,‘牛牛‘,‘女‘,29,‘1989-12-24‘,100,55,98);
/*查询所有列*/
SELECT * FROM class0328
/*查询指定列*/
SELECT id,cname FROM class0328;
/*添加常量列(将id在查询时改名为编号显示....）*/
SELECT id AS ‘编号‘,cname AS ‘学生姓名‘ FROM class0328;
/*查询时合并列*/
SELECT cname,(html+js) AS ‘前端成绩‘ FROM class0328;
/*查询去除重复记录*/
SELECT sex FROM class0328(重复查询了）；
SELECT DISTINCT sex FROM class0328;
/*条件查询*/
SELECT * FROM class0328 WHERE id=1 AND sex=‘男‘;
/*，，*，，代表所有，可以替换单个属性例如姓名、年龄等*/
SELECT cname FROM class0328 WHERE id=1 AND sex=‘男‘;
/*或着查询*/
SELECT * FROM class0328 WHERE sex=‘男‘ OR age=25;
/*比较条件(>,<,>=,<=,=,<>(不等于))*/
SELECT cname FROM class0328 WHERE html>60;
SELECT *FROM class0328 WHERE js<>100;
/*下面俩意义一样*/
SELECT * FROM class0328 WHERE html>=0 AND html<=60;
SELECT * FROM class0328 WHERE html BETWEEN 0 AND 60;
INSERT INTO class0328 VALUES(8,‘牛孙‘,‘‘,29,‘1989-12-24‘,100,20,98);
/*判断性别不为空的数据*/
SELECT * FROM class0328 WHERE sex IS NULL;
SELECT * FROM class0328 WHERE sex <>‘‘;
SELECT * FROM class0328 WHERE sex =‘‘;
SELECT * FROM class0328 WHERE sex IS NOT NULL AND sex<>‘‘;
/*模糊查询(表里姓张的都查询）(%表示任意字符）（_表示一个任意字符）*/
SELECT * FROM class0328 WHERE cname LIKE ‘张%‘;
SELECT * FROM class0328 WHERE cname LIKE ‘王__‘;
SELECT * FROM class0328 WHERE cname LIKE ‘__臣‘;
/*聚合函数*/
SELECT SUM(html) AS ‘htmlscore‘ FROM class0328;
SELECT SUM(html+js) FROM class0328;
/*平均成绩*/
SELECT AVG(html)AS‘平均成绩‘ FROM class0328;
SELECT MAX(js)AS ‘js最高分‘ FROM class0328;
SELECT cname,MIN(js)AS ‘js低高分‘ FROM class0328;
/*有多少条*/
SELECT COUNT(sex) FROM class0328;
SELECT * FROM class0328 LIMIT 0,2;
SELECT * FROM class0328 LIMIT 3,2;