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MySQL之CRUD
2022-07-05 14:45:00 【安离九歌】
目录
前言
上次分享了MySQL的账户管理，这次我们要分享的内容是CRUD，不管怎么样CRUD总要会点吧。
一、基本查询
#1.查询表中的单个字段
SELECT department_id FROM t_mysql_employees
#2.查询表中的多个字段
SELECT department_id,employee_id FROM t_mysql_employees
#3.查询表中的所有字段
SELECT * FROM t_mysql_employees
#4.查询常量值
SELECT 100;
SELECT 'john';
#5.查询表达式
SELECT 100%98;
#6.查询函数
SELECT VERSION();
#7.起别名
SELECT department_id 部门编号 FROM t_mysql_employees
#8.去重
SELECT DISTINCT department_id FROM t_mysql_employees
#案例：查询员工表中涉及到的所有的部门编号
SELECT DISTINCT department_id FROM t_mysql_employees
#9.+号的作用
SELECT 'join'+1
SELECT '100'+1运行结果：
#1.查询表中的单个字段
#2.查询表中的多个字段
#3.查询表中的所有字段
#4.查询常量值
SELECT 100;
SELECT 'john';
#5.查询表达式
SELECT 100%98;
#6.查询函数
SELECT VERSION();
#7.起别名
#8.去重
#9.+号的作用
二、过滤查询
#一、按条件表达式筛选
#案例1：查询工资>12000的员工信息
SELECT * FROM t_mysql_employees WHERE salary > 12000
#案例2：查询部门编号不等于90号的员工名和部门编号
SELECT first_name,department_id FROM t_mysql_employees WHERE NOT(department_id=90)
#二、按逻辑表达式筛选
#案例1：查询工资z在10000到20000之间的员工名、工资以及奖金
SELECT first_name,salary,commission_pct FROM t_mysql_employees WHERE salary BETWEEN 10000 AND 20000
#案例2：查询部门编号不是在90到110之间，或者工资高于15000的员工信息
SELECT * FROM t_mysql_employees WHERE NOT(department_id BETWEEN 90 AND 110) or salary > 12000
#三、模糊查询
#1.like
#案例1：查询员工名中包含字符a的员工信息
SELECT * FROM t_mysql_employees WHERE first_name LIKE '%a%'
#案例2：查询员工名中第三个字符为e，第五个字符为a的员工名和工资
SELECT * FROM t_mysql_employees WHERE first_name LIKE '__e_a%'
#案例3：查询员工名中第二个字符为_的员工性
SELECT * FROM t_mysql_employees WHERE last_name LIKE
#2.between and
#案例1：查询员工编号在100到120之间的员工信息
SELECT * FROM t_mysql_employees WHERE employee_id BETWEEN 100 AND 120
#3.in
#案例：查询员工的工种编号是 IT_PROG、AD_VP、AD_PRES中的一个员工名和工种编号
SELECT first_name,job_id FROM t_mysql_employees WHERE job_id IN ('IT_PROG','AD_VP','AD_PRES')
#4、is null
#案例1：查询没有奖金的员工名和奖金率
SELECT first_name,commission_pct FROM t_mysql_employees WHERE commission_pct is null
#案例2：查询有奖金的员工名和奖金率
SELECT first_name,commission_pct FROM t_mysql_employees WHERE not commission_pct is null
#安全等于 <=>
#案例1：查询没有奖金的员工名和奖金率
SELECT first_name,commission_pct FROM t_mysql_employees WHERE commission_pct <=> null
#案例2：查询工资为12000的员工信息
SELECT * FROM t_mysql_employees WHERE salary <=>12000
#is null pk <=>
IS NULL:仅仅可以判断NULL值，可读性较高，建议使用
<=> :既可以判断NULL值，又可以判断普通的数值，可读性较低一、按条件表达式筛选
#案例1：查询工资>12000的员工信息
#案例2：查询部门编号不等于90号的员工名和部门编号
#二、按逻辑表达式筛选
#案例1：查询工资z在10000到20000之间的员工名、工资以及奖金
#案例2：查询部门编号不是在90到110之间，或者工资高于15000的员工信息
#三、模糊查询
#1.like
#案例1：查询员工名中包含字符a的员工信息
#案例2：查询员工名中第三个字符为e，第五个字符为a的员工名和工资
#2.between and
#案例1：查询员工编号在100到120之间的员工信息
#3.in
#案例：查询员工的工种编号是 IT_PROG、AD_VP、AD_PRES中的一个员工名和工种编号
#4、is null
#案例1：查询没有奖金的员工名和奖金率
#案例2：查询有奖金的员工名和奖金率
#安全等于 <=>
#案例1：查询没有奖金的员工名和奖金率
#案例2：查询工资为12000的员工信息
#is null pk <=>
IS NULL:仅仅可以判断NULL值，可读性较高，建议使用
<=> :既可以判断NULL值，又可以判断普通的数值，可读性较低
三、排序
order by 子句
#1、按单个字段排序
#案例：按员工表薪资排序
SELECT * FROM t_mysql_employees ORDER BY salary
#2、添加筛选条件再排序
#案例：查询部门编号>=90的员工信息，并按员工编号降序
SELECT * FROM t_mysql_employees WHERE department_id>=90 ORDER BY employee_id DESC
#3、按表达式排序
#案例：查询员工信息 按年薪降序
SELECT em.salary*12*(1+IFNULL(commission_pct,0)),em.* FROM t_mysql_employees em ORDER BY em.salary*12*(1+IFNULL(commission_pct,0)) DESC
#4、按别名排序
#案例：查询员工信息 按年薪升序
SELECT em.salary*12*(1+IFNULL(commission_pct,0)),em.* FROM t_mysql_employees em ORDER BY em.salary*12*(1+IFNULL(commission_pct,0)) ASC
#5、按函数排序
#案例：查询员工名，并且按名字的长度降序
SELECT first_name FROM t_mysql_employees ORDER BY LENGTH(first_name) DESC
#6、按多个字段排序
#案例：查询员工信息，要求先按工资降序，再按employee_id升序
SELECT * FROM t_mysql_employees ORDER BY salary DESC,employee_id ASC
#1.查询员工的姓名和部门号和年薪，按年薪降序 按姓名升序
SELECT em.first_name,em.department_id,em.salary*12*(1+IFNULL(commission_pct,0)) FROM t_mysql_employees em ORDER BY em.salary*12(1+IFNULL(commission_pct,0)) DESC,first_name asc
#2.选择工资不在8000到17000的员工的姓名和工资，按工资降序
SELECT first_name,salary FROM t_mysql_employees WHERE NOT(salary BETWEEN 8000 AND 17000) ORDER BY salary desc
#3.查询邮箱中包含e的员工信息，并先按邮箱的字节数降序，再按部门号升序
SELECT * FROM t_mysql_employees WHERE email LIKE '%e%' ORDER BY LENGTH(email)DESC,department_id ASCorder by 子句
#1、按单个字段排序
#案例：按员工表薪资排序
#2、添加筛选条件再排序
#案例：查询部门编号>=90的员工信息，并按员工编号降序
#3、按表达式排序
#案例：查询员工信息 按年薪降序
#4、按别名排序
#案例：查询员工信息 按年薪升序
#5、按函数排序
#案例：查询员工名，并且按名字的长度降序
#6、按多个字段排序
#案例：查询员工信息，要求先按工资降序，再按employee_id升序
#1.查询员工的姓名和部门号和年薪，按年薪降序 按姓名升序
#2.选择工资不在8000到17000的员工的姓名和工资，按工资降序
#3.查询邮箱中包含e的员工信息，并先按邮箱的字节数降序，再按部门号升序
四、案例
·insert into t_student values('01' , '赵雷' , '1990-01-01' , '男');
insert into t_student values('02' , '钱电' , '1990-12-21' , '男');
insert into t_student values('03' , '孙风' , '1990-12-20' , '男');
insert into t_student values('04' , '李云' , '1990-12-06' , '男');
insert into t_student values('05' , '周梅' , '1991-12-01' , '女');
insert into t_student values('06' , '吴兰' , '1992-01-01' , '女');
insert into t_student values('07' , '郑竹' , '1989-01-01' , '女');
insert into t_student values('09' , '张三' , '2017-12-20' , '女');
insert into t_student values('10' , '李四' , '2017-12-25' , '女');
insert into t_student values('11' , '李四' , '2012-06-06' , '女');
insert into t_student values('12' , '赵六' , '2013-06-13' , '女');
insert into t_student values('13' , '孙七' , '2014-06-01' , '女');
-- 教师表
insert into t_teacher values('01' , '张三');
insert into t_teacher values('02' , '李四');
insert into t_teacher values('03' , '王五');
-- 课程表
insert into t_course values('01' , '语文' , '02');
insert into t_course values('02' , '数学' , '01');
insert into t_course values('03' , '英语' , '03');
-- 成绩表
insert into t_score values('01' , '01' , 80);
insert into t_score values('01' , '02' , 90);
insert into t_score values('01' , '03' , 99);
insert into t_score values('02' , '01' , 70);
insert into t_score values('02' , '02' , 60);
insert into t_score values('02' , '03' , 80);
insert into t_score values('03' , '01' , 80);
insert into t_score values('03' , '02' , 80);
insert into t_score values('03' , '03' , 80);
insert into t_score values('04' , '01' , 50);
insert into t_score values('04' , '02' , 30);
insert into t_score values('04' , '03' , 20);
insert into t_score values('05' , '01' , 76);
insert into t_score values('05' , '02' , 87);
insert into t_score values('06' , '01' , 31);
insert into t_score values('06' , '03' , 34);
insert into t_score values('07' , '02' , 89);
insert into t_score values('07' , '03' , 98);
#01）查询" 01 "课程比" 02"课程成绩高的学生的信息及课程分数
SELECT st.*,sc.score AS '01',sc2.score AS '02' FROM t_student st
LEFT JOIN t_score sc ON sc.sid=st.sid AND sc.cid='01'
LEFT JOIN t_score sc2 ON sc2.sid=st.sid AND sc2.cid='02'
WHERE sc.score>sc2.score
#02）查询同时存在" 01 "课程和" 02 "课程的情况
SELECT st.* FROM t_student st INNER JOIN t_score sc ON sc.sid=st.sid AND sc.cid='01'
WHERE st.sid IN (
SELECT st2.sid FROM t_student st2 INNER JOIN t_score sc2 ON sc2.sid=st2.sid AND sc2.cid='02'
)
#03）查询存在" 01 "课程但可能不存在" 02 "课程的情况(不存在时显示为 null )
SELECT st.* FROM t_student st INNER JOIN t_score sc ON sc.sid=st.sid AND sc.cid='01'
WHERE st.sid NOT IN (
SELECT st2.sid FROM t_student st2 INNER JOIN t_score sc2 ON sc2.sid=st2.sid AND sc2.cid='02'
)
#04）查询不存在" 01 "课程但存在" 02 "课程的情况
SELECT * FROM t_student st INNER JOIN t_score sc ON sc.sid=st.sid AND sc.cid='02'
WHERE st.sid NOT IN (
SELECT st2.sid FROM t_student st2 INNER JOIN t_score sc2 ON sc2.sid=st2.sid AND sc2.cid='01'
)
#05）查询平均成绩大于等于 60 分的同学的学生编号和学生姓名和平均成绩
SELECT st.sid,st.sname,ROUND(AVG(sc.score),2) 平均分
FROM t_student st
LEFT JOIN t_score sc ON st.sid=sc.sid
GROUP BY st.sid HAVING AVG(sc.score)>=60;
#06）查询在t_score表存在成绩的学生信息
SELECT st.* FROM t_student st WHERE sid IN(
SELECT sc.sid FROM t_score sc
)
#07）查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩(没成绩的显示为 null )
SELECT st.sid,st.sname,COUNT(sc.cid),ROUND(SUM(sc.score),2) AS '总成绩' FROM t_student st
LEFT JOIN t_score sc ON sc.sid=st.sid GROUP BY st.sid
#08）查询「李」姓老师的数量
SELECT COUNT(*) FROM t_teacher WHERE tname LIKE '李%'
#09）查询学过「张三」老师授课的同学的信息
SELECT st.* FROM t_student st WHERE sid IN(
SELECT sid FROM t_score WHERE cid = (
SELECT cid FROM t_course WHERE tid = (
SELECT tid FROM t_teacher WHERE tname = '张三'
)
)
)
#10）查询没有学全所有课程的同学的信息
SELECT st.*FROM t_student st WHERE sid NOT IN(
SELECT sid FROM t_score GROUP BY sid HAVING COUNT(cid)>=(SELECT COUNT(cid) FROM t_course)
)
#11）查询没学过"张三"老师讲授的任一门课程的学生姓名
SELECT st.sname FROM t_student st WHERE st.sid NOT IN (
SELECT sc.sid FROM t_score sc
INNER JOIN t_course c ON c.cid=sc.cid
INNER JOIN t_teacher t ON t.tid=c.tid AND t.tname="张三"
)
#12）查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩
SELECT st.sid,st.sname,AVG(sc.score) FROM t_student st
LEFT JOIN t_score sc ON sc.sid=st.sid WHERE sc.sid IN(
SELECT sc.sid FROM t_score sc WHERE sc.score<60 OR sc.score IS NULL GROUP BY sc.sid HAVING COUNT(1)>=2
)
GROUP BY st.sid
#13）检索" 01 "课程分数小于 60，按分数降序排列的学生信息
SELECT st.*,sc.score FROM t_student st LEFT JOIN t_score sc ON sc.sid=st.sid WHERE sc.cid='01' AND sc.score<60 ORDER BY sc.score DESC ;
#14）按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩
SELECT st.sid,st.sname,
(IFNULL((sc4.score),0)) "平均分",
(IFNULL((sc.score),0)) "语文",
(IFNULL((sc2.score),0)) "数学",
(IFNULL((sc3.score),0))"英语"
FROM t_student st
LEFT JOIN t_score sc ON sc.sid=st.sid AND sc.cid="01"
LEFT JOIN t_score sc2 ON sc2.sid=st.sid AND sc2.cid="02"
LEFT JOIN t_score sc3 ON sc3.sid=st.sid AND sc3.cid="03"
LEFT JOIN t_score sc4 ON sc4.sid=st.sid
GROUP BY st.sid
ORDER BY AVG(sc4.score) DESC
#15）查询各科成绩最高分、最低分和平均分：
#以如下形式显示：课程 ID，课程 name，最高分，最低分，平均分，及格率，中等率，优良率，优秀率及格为>=60，中等为：70-80，优良为：80-90，优秀为：>=90
#要求输出课程号和选修人数，查询结果按人数降序排列，若人数相同，按课程号升序排列
SELECT c.cid,c.cname,MAX(sc.score) "最高分",MIN(sc.score) "最低分",AVG(sc.score) "平均分"
,((SELECT COUNT(sid) FROM t_score WHERE score>=60 AND cid=c.cid )/(SELECT COUNT(sid) FROM t_score WHERE cid=c.cid)) "及格率"
,((SELECT COUNT(sid) FROM t_score WHERE score>=70 AND score<80 AND cid=c.cid )/(SELECT COUNT(sid) FROM t_score WHERE cid=c.cid)) "中等率"
,((SELECT COUNT(sid) FROM t_score WHERE score>=80 AND score<90 AND cid=c.cid )/(SELECT COUNT(sid) FROM t_score WHERE cid=c.cid)) "优良率"
,((SELECT COUNT(sid) FROM t_score WHERE score>=90 AND cid=c.cid )/(SELECT COUNT(sid) FROM t_score WHERE cid=c.cid)) "优秀率"
FROM t_course c
LEFT JOIN t_score sc ON sc.cid=c.cid
GROUP BY c.cid
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