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MySQL之CRUD
2022-07-05 14:49:00 【安離九歌】
目錄
前言
上次分享了MySQL的賬戶管理，這次我們要分享的內容是CRUD，不管怎麼樣CRUD總要會點吧。
一、基本查詢
#1.查詢錶中的單個字段
SELECT department_id FROM t_mysql_employees
#2.查詢錶中的多個字段
SELECT department_id,employee_id FROM t_mysql_employees
#3.查詢錶中的所有字段
SELECT * FROM t_mysql_employees
#4.查詢常量值
SELECT 100;
SELECT 'john';
#5.查詢錶達式
SELECT 100%98;
#6.查詢函數
SELECT VERSION();
#7.起別名
SELECT department_id 部門編號 FROM t_mysql_employees
#8.去重
SELECT DISTINCT department_id FROM t_mysql_employees
#案例：查詢員工錶中涉及到的所有的部門編號
SELECT DISTINCT department_id FROM t_mysql_employees
#9.+號的作用
SELECT 'join'+1
SELECT '100'+1運行結果：
#1.查詢錶中的單個字段
#2.查詢錶中的多個字段
#3.查詢錶中的所有字段
#4.查詢常量值
SELECT 100;
SELECT 'john';
#5.查詢錶達式
SELECT 100%98;
#6.查詢函數
SELECT VERSION();
#7.起別名
#8.去重
#9.+號的作用
二、過濾查詢
#一、按條件錶達式篩選
#案例1：查詢工資>12000的員工信息
SELECT * FROM t_mysql_employees WHERE salary > 12000
#案例2：查詢部門編號不等於90號的員工名和部門編號
SELECT first_name,department_id FROM t_mysql_employees WHERE NOT(department_id=90)
#二、按邏輯錶達式篩選
#案例1：查詢工資z在10000到20000之間的員工名、工資以及獎金
SELECT first_name,salary,commission_pct FROM t_mysql_employees WHERE salary BETWEEN 10000 AND 20000
#案例2：查詢部門編號不是在90到110之間，或者工資高於15000的員工信息
SELECT * FROM t_mysql_employees WHERE NOT(department_id BETWEEN 90 AND 110) or salary > 12000
#三、模糊查詢
#1.like
#案例1：查詢員工名中包含字符a的員工信息
SELECT * FROM t_mysql_employees WHERE first_name LIKE '%a%'
#案例2：查詢員工名中第三個字符為e，第五個字符為a的員工名和工資
SELECT * FROM t_mysql_employees WHERE first_name LIKE '__e_a%'
#案例3：查詢員工名中第二個字符為_的員工性
SELECT * FROM t_mysql_employees WHERE last_name LIKE
#2.between and
#案例1：查詢員工編號在100到120之間的員工信息
SELECT * FROM t_mysql_employees WHERE employee_id BETWEEN 100 AND 120
#3.in
#案例：查詢員工的工種編號是 IT_PROG、AD_VP、AD_PRES中的一個員工名和工種編號
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：查詢沒有獎金的員工名和獎金率
SELECT first_name,commission_pct FROM t_mysql_employees WHERE commission_pct is null
#案例2：查詢有獎金的員工名和獎金率
SELECT first_name,commission_pct FROM t_mysql_employees WHERE not commission_pct is null
#安全等於 <=>
#案例1：查詢沒有獎金的員工名和獎金率
SELECT first_name,commission_pct FROM t_mysql_employees WHERE commission_pct <=> null
#案例2：查詢工資為12000的員工信息
SELECT * FROM t_mysql_employees WHERE salary <=>12000
#is null pk <=>
IS NULL:僅僅可以判斷NULL值，可讀性較高，建議使用
<=> :既可以判斷NULL值，又可以判斷普通的數值，可讀性較低一、按條件錶達式篩選
#案例1：查詢工資>12000的員工信息
#案例2：查詢部門編號不等於90號的員工名和部門編號
#二、按邏輯錶達式篩選
#案例1：查詢工資z在10000到20000之間的員工名、工資以及獎金
#案例2：查詢部門編號不是在90到110之間，或者工資高於15000的員工信息
#三、模糊查詢
#1.like
#案例1：查詢員工名中包含字符a的員工信息
#案例2：查詢員工名中第三個字符為e，第五個字符為a的員工名和工資
#2.between and
#案例1：查詢員工編號在100到120之間的員工信息
#3.in
#案例：查詢員工的工種編號是 IT_PROG、AD_VP、AD_PRES中的一個員工名和工種編號
#4、is null
#案例1：查詢沒有獎金的員工名和獎金率
#案例2：查詢有獎金的員工名和獎金率
#安全等於 <=>
#案例1：查詢沒有獎金的員工名和獎金率
#案例2：查詢工資為12000的員工信息
#is null pk <=>
IS NULL:僅僅可以判斷NULL值，可讀性較高，建議使用
<=> :既可以判斷NULL值，又可以判斷普通的數值，可讀性較低
三、排序
order by 子句
#1、按單個字段排序
#案例：按員工錶薪資排序
SELECT * FROM t_mysql_employees ORDER BY salary
#2、添加篩選條件再排序
#案例：查詢部門編號>=90的員工信息，並按員工編號降序
SELECT * FROM t_mysql_employees WHERE department_id>=90 ORDER BY employee_id DESC
#3、按錶達式排序
#案例：查詢員工信息 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、按別名排序
#案例：查詢員工信息 按年薪昇序
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、按函數排序
#案例：查詢員工名，並且按名字的長度降序
SELECT first_name FROM t_mysql_employees ORDER BY LENGTH(first_name) DESC
#6、按多個字段排序
#案例：查詢員工信息，要求先按工資降序，再按employee_id昇序
SELECT * FROM t_mysql_employees ORDER BY salary DESC,employee_id ASC
#1.查詢員工的姓名和部門號和年薪，按年薪降序 按姓名昇序
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.選擇工資不在8000到17000的員工的姓名和工資，按工資降序
SELECT first_name,salary FROM t_mysql_employees WHERE NOT(salary BETWEEN 8000 AND 17000) ORDER BY salary desc
#3.查詢郵箱中包含e的員工信息，並先按郵箱的字節數降序，再按部門號昇序
SELECT * FROM t_mysql_employees WHERE email LIKE '%e%' ORDER BY LENGTH(email)DESC,department_id ASCorder by 子句
#1、按單個字段排序
#案例：按員工錶薪資排序
#2、添加篩選條件再排序
#案例：查詢部門編號>=90的員工信息，並按員工編號降序
#3、按錶達式排序
#案例：查詢員工信息 按年薪降序
#4、按別名排序
#案例：查詢員工信息 按年薪昇序
#5、按函數排序
#案例：查詢員工名，並且按名字的長度降序
#6、按多個字段排序
#案例：查詢員工信息，要求先按工資降序，再按employee_id昇序
#1.查詢員工的姓名和部門號和年薪，按年薪降序 按姓名昇序
#2.選擇工資不在8000到17000的員工的姓名和工資，按工資降序
#3.查詢郵箱中包含e的員工信息，並先按郵箱的字節數降序，再按部門號昇序
四、案例
·insert into t_student values('01' , '趙雷' , '1990-01-01' , '男');
insert into t_student values('02' , '錢電' , '1990-12-21' , '男');
insert into t_student values('03' , '孫風' , '1990-12-20' , '男');
insert into t_student values('04' , '李雲' , '1990-12-06' , '男');
insert into t_student values('05' , '周梅' , '1991-12-01' , '女');
insert into t_student values('06' , '吳蘭' , '1992-01-01' , '女');
insert into t_student values('07' , '鄭竹' , '1989-01-01' , '女');
insert into t_student values('09' , '張三' , '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' , '趙六' , '2013-06-13' , '女');
insert into t_student values('13' , '孫七' , '2014-06-01' , '女');
-- 教師錶
insert into t_teacher values('01' , '張三');
insert into t_teacher values('02' , '李四');
insert into t_teacher values('03' , '王五');
-- 課程錶
insert into t_course values('01' , '語文' , '02');
insert into t_course values('02' , '數學' , '01');
insert into t_course values('03' , '英語' , '03');
-- 成績錶
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）查詢" 01 "課程比" 02"課程成績高的學生的信息及課程分數
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）查詢同時存在" 01 "課程和" 02 "課程的情况
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）查詢存在" 01 "課程但可能不存在" 02 "課程的情况(不存在時顯示為 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）查詢不存在" 01 "課程但存在" 02 "課程的情况
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）查詢平均成績大於等於 60 分的同學的學生編號和學生姓名和平均成績
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）查詢在t_score錶存在成績的學生信息
SELECT st.* FROM t_student st WHERE sid IN(
SELECT sc.sid FROM t_score sc
)
#07）查詢所有同學的學生編號、學生姓名、選課總數、所有課程的總成績(沒成績的顯示為 null )
SELECT st.sid,st.sname,COUNT(sc.cid),ROUND(SUM(sc.score),2) AS '總成績' FROM t_student st
LEFT JOIN t_score sc ON sc.sid=st.sid GROUP BY st.sid
#08）查詢「李」姓老師的數量
SELECT COUNT(*) FROM t_teacher WHERE tname LIKE '李%'
#09）查詢學過「張三」老師授課的同學的信息
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 = '張三'
)
)
)
#10）查詢沒有學全所有課程的同學的信息
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）查詢沒學過"張三"老師講授的任一門課程的學生姓名
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="張三"
)
#12）查詢兩門及其以上不及格課程的同學的學號，姓名及其平均成績
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）檢索" 01 "課程分數小於 60，按分數降序排列的學生信息
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）按平均成績從高到低顯示所有學生的所有課程的成績以及平均成績
SELECT st.sid,st.sname,
(IFNULL((sc4.score),0)) "平均分",
(IFNULL((sc.score),0)) "語文",
(IFNULL((sc2.score),0)) "數學",
(IFNULL((sc3.score),0))"英語"
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）查詢各科成績最高分、最低分和平均分：
#以如下形式顯示：課程 ID，課程 name，最高分，最低分，平均分，及格率，中等率，優良率，優秀率及格為>=60，中等為：70-80，優良為：80-90，優秀為：>=90
#要求輸出課程號和選修人數，查詢結果按人數降序排列，若人數相同，按課程號昇序排列
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)) "優良率"
,((SELECT COUNT(sid) FROM t_score WHERE score>=90 AND cid=c.cid )/(SELECT COUNT(sid) FROM t_score WHERE cid=c.cid)) "優秀率"
FROM t_course c
LEFT JOIN t_score sc ON sc.cid=c.cid
GROUP BY c.cid
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