数据库小练习2

1.创建数据库java123

2.使用数据库java123

3.创建表stu

4.新增数据

#创建数据库java123
CREATE DATABASE IF NOT EXISTS java123;

#使用数据库java123
USE java123;

#创建表stu
CREATE TABLE stu (
	sid	CHAR(6),
	sname VARCHAR(50),
	age INT,
	gender VARCHAR(50)
);

#新增数据
INSERT INTO stu VALUES('S_1001', 'liuYi', 35, 'male');
INSERT INTO stu VALUES('S_1002', 'chenEr', 15, 'female');
INSERT INTO stu VALUES('S_1003', 'zhangSan', 95, 'male');
INSERT INTO stu VALUES('S_1004', 'liSi', 65, 'female');
INSERT INTO stu VALUES('S_1005', 'wangWu', 55, 'male');
INSERT INTO stu VALUES('S_1006', 'zhaoLiu', 75, 'female');
INSERT INTO stu VALUES('S_1007', 'sunQi', 25, 'male');
INSERT INTO stu VALUES('S_1008', 'zhouBa', 45, 'female');
INSERT INTO stu VALUES('S_1009', 'wuJiu', 85, 'male');
INSERT INTO stu VALUES('S_1010', 'zhengShi', 5, 'female');
INSERT INTO stu VALUES('S_1011', 'xxx', NULL, NULL);
INSERT INTO stu VALUES('S_1012', NULL, NULL, NULL);

 结果如下：

 5.创建表emp，并添加数据

CREATE TABLE emp(
	empno INT,
	ename VARCHAR(50),
	job VARCHAR(50),
	mgr INT,
	hiredate DATE,
	sal	DECIMAL(7,2),
	comm decimal(7,2),
	deptno INT
) ;

INSERT INTO emp values(7369,'SMITH','CLERK',7902,'1980-12-17',800,NULL,20);
INSERT INTO emp values(7499,'ALLEN','SALESMAN',7698,'1981-02-20',1600,300,30);
INSERT INTO emp values(7521,'WARD','SALESMAN',7698,'1981-02-22',1250,500,30);
INSERT INTO emp values(7566,'JONES','MANAGER',7839,'1981-04-02',2975,NULL,20);
INSERT INTO emp values(7654,'MARTIN','SALESMAN',7698,'1981-09-28',1250,1400,30);
INSERT INTO emp values(7698,'BLAKE','MANAGER',7839,'1981-05-01',2850,NULL,30);
INSERT INTO emp values(7782,'CLARK','MANAGER',7839,'1981-06-09',2450,NULL,10);
INSERT INTO emp values(7788,'SCOTT','ANALYST',7566,'1987-04-19',3000,NULL,20);
INSERT INTO emp values(7839,'KING','PRESIDENT',NULL,'1981-11-17',5000,NULL,10);
INSERT INTO emp values(7844,'TURNER','SALESMAN',7698,'1981-09-08',1500,0,30);
INSERT INTO emp values(7876,'ADAMS','CLERK',7788,'1987-05-23',1100,NULL,20);
INSERT INTO emp values(7900,'JAMES','CLERK',7698,'1981-12-03',950,NULL,30);
INSERT INTO emp values(7902,'FORD','ANALYST',7566,'1981-12-03',3000,NULL,20);
INSERT INTO emp values(7934,'MILLER','CLERK',7782,'1982-01-23',1300,NULL,10);

结果如下：

 6.创建dept表，并添加数据

CREATE TABLE dept(
	deptno INT,
	dname varchar(14),
	loc varchar(13)
);

INSERT INTO dept values(10, 'ACCOUNTING', 'NEW YORK');
INSERT INTO dept values(20, 'RESEARCH', 'DALLAS');
INSERT INTO dept values(30, 'SALES', 'CHICAGO');
INSERT INTO dept values(40, 'OPERATIONS', 'BOSTON');

结果如下：

 SQL语句训练：

#查询性别为女，并且年龄50的记录
SELECT * FROM stu WHERE gender = 'female' AND age < 50;
#查询学号为S_1001，或者姓名为liSi的记录
SELECT * FROM stu WHERE sid = 'S_1001' OR sname = 'lisi';
#查询学号为S_1001，S_1002，S_1003的记录
SELECT * FROM stu WHERE sid IN('S_1001','S_1002','S_1003');
SELECT * FROM stu WHERE sid = 'S_1001' OR sid = 'S_1002' OR sid = 'S_1003';
#查询学号不是S_1001，S_1002，S_1003的记录
SELECT * FROM stu WHERE sid NOT IN('S_1001','S_1002','S_1003');
#查询年龄为null的记录
SELECT * FROM stu WHERE age IS NULL;
#查询年龄在20到40之间的学生记录
SELECT * FROM stu WHERE age >= 20 AND age <= 40;
SELECT * FROM stu WHERE age BETWEEN 20 AND 40;
#查询性别非男的学生记录
SELECT * FROM stu WHERE gender != 'male';
SELECT * FROM stu WHERE gender <> 'male';
SELECT * FROM stu WHERE NOT gender = 'male';
SELECT * FROM stu WHERE gender = 'female';
#查询姓名不为null的学生记录
SELECT * FROM stu WHERE sname IS NOT NULL;
SELECT * FROM stu WHERE NOT sname IS NULL;
#查询姓名由5个字母构成的学生记录
SELECT * FROM stu WHERE sname LIKE '_____';
#查询姓名由5个字母构成，并且第5个字母为“i”的学生记录
SELECT * FROM stu WHERE sname LIKE '____i';
#查询姓名以“z”开头的学生记录
SELECT * FROM stu WHERE sname LIKE 'z%';
#查询姓名中第2个字母为“i”的学生记录
SELECT * FROM stu WHERE sname LIKE '_i%';
#查询姓名中包含“a”字母的学生记录
SELECT * FROM stu WHERE sname LIKE '%a%';

#去除重复记录 DISTINCT
SELECT DISTINCT sal FROM emp;
#查看雇员的月薪与佣金之和
SELECT *,sal+comm FROM emp;#有问题的写法（SQL语句运算存在null的话结果为null）
SELECT *, sal+IFNULL(comm,0)FROM emp;#正确的写法
#给列名添加别名
SELECT *, sal+ IFNULL(comm,0) AS '月薪与佣金和' FROM emp;
SELECT *, sal+ IFNULL(comm,0)  '月薪与佣金和' FROM emp;#不推荐使用
#排序
#查询所有学生记录，按年龄升序排序
SELECT * FROM stu ORDER BY age ASC;#升序
SELECT * FROM stu ORDER BY age;#升序
#查询所有学生记录，按年龄降序排序
SELECT * FROM stu ORDER BY age DESC;#降序
#查询所有雇员，按月薪降序排序，如果月薪相同时，按编号升序排序
SELECT * FROM emp ORDER BY sal DESC,empno ASC;
#聚合函数  sum avg max min count
#查询emp表中记录数
SELECT COUNT(*) FROM emp;
#查询emp表中有佣金的人数：
SELECT COUNT(comm) FROM emp;
#查询emp表中月薪大于2500的人数：
SELECT COUNT(*) FROM emp WHERE sal>2500;
#统计月薪与佣金之和大于2500元的人数
SELECT COUNT(*) FROM emp WHERE sal+IFNULL(comm,0) >2500;
#查询有佣金的人数，以及有领导的人数
SELECT COUNT(comm),COUNT(mgr) FROM emp;
#查询所有雇员月薪和
SELECT SUM(sal) FROM emp;
#查询所有雇员月薪和，以及所有雇员佣金和：
SELECT SUM(sal),SUM(comm) FROM emp;
#查询所有雇员月薪+佣金和
SELECT SUM(sal+IFNULL(comm,0)) FROM emp;
#统计所有员工平均工资
SELECT AVG(sal) FROM emp;
#查询最高工资和最低工资
SELECT MAX(sal) AS '最高工资',MIN(sal) AS '最低工资' FROM emp;