創(chuàng)建表

create table employee(

id intnotnull unique auto_increment,

name varchar(20) notnull,

sex enum('male','female') not null default 'male', #大部分是男的

age int(3) unsigned not null default 28,

hire_date datenotnull,

post varchar(50),

post_comment varchar(100),

salary double(15,2),

office int,#一個(gè)部門一個(gè)屋子

depart_id int

);

插入記錄

insert into employee(name,sex,age,hire_date,post,salary,office,depart_id) values

('egon','male',18,'20170301','老男孩駐沙河辦事處外交大使',7300.33,401,1), #以下是教學(xué)部，全都是老師

('alex','male',78,'20150302','teacher',1000000.31,401,1),

('wupeiqi','male',81,'20130305','teacher',8300,401,1),

('yuanhao','male',73,'20140701','teacher',3500,401,1),

('liwenzhou','male',28,'20121101','teacher',2100,401,1),

('jingliyang','female',18,'20110211','teacher',9000,401,1),

('jinxin','male',18,'19000301','teacher',30000,401,1),

('成龍','male',48,'20101111','teacher',10000,401,1),

('歪歪','female',48,'20150311','sale',3000.13,402,2),#以下是銷售部門

('丫丫','female',38,'20101101','sale',2000.35,402,2),

('丁丁','female',18,'20110312','sale',1000.37,402,2),

('星星','female',18,'20160513','sale',3000.29,402,2),

('格格','female',28,'20170127','sale',4000.33,402,2),

('張野','male',28,'20160311','operation',10000.13,403,3), #以下是運(yùn)營(yíng)部門

('程咬金','male',18,'19970312','operation',20000,403,3),

('程咬銀','female',18,'20130311','operation',19000,403,3),

('程咬銅','male',18,'20150411','operation',18000,403,3),

('程咬鐵','female',18,'20140512','operation',17000,403,3);

語(yǔ)法

SELECT distinct 字段1,字段2 from庫(kù)名.表名

where 條件#查找符合條件的記錄

GROUP BY field(字段) #分組

HAVING 篩選 #過濾

ORDER BY field(字段) #按照后邊的字段進(jìn)行排序

LIMIT 限制條數(shù) #限制顯示條數(shù)

關(guān)鍵字的執(zhí)行優(yōu)先級(jí)

fromwhere

group by

select

distinct

having

order by

limit1.找到表:from

2.拿著where指定的約束條件，去文件/表中取出一條條記錄3.將取出的一條條記錄進(jìn)行分組group by，如果沒有g(shù)roup by，則整體作為一組4.執(zhí)行select(去重)5.將分組的結(jié)果進(jìn)行having過濾6.將結(jié)果按條件排序：order by7.限制結(jié)果的顯示條數(shù)

單表查詢

select 字段1,字段2 from 表名;

字段查詢?nèi)ブ豥istinct

select distinct post,sex from employee;

查詢字段數(shù)據(jù)并計(jì)算(四則運(yùn)算:加減乘除都可以)

SELECT name, salary*12 FROM employee;

給顯示的字段重命名

SELECT name, salary*12 Annual_salary FROM employee;

CONCAT: 就是做字符串拼接的,并且拼接之后的結(jié)果

select concat('姓名:',name,'年薪:',salary*12) Text from employee;

CONCAT_WS(): 第一個(gè)參數(shù)為分隔符來進(jìn)行字符串拼接

SELECT CONCAT_WS(':',name,salary*12) AS Annual_salary fromemployee;

SELECT CONCAT(name,':',salary*12) Annual_salary from employee;

WHERE約束

where 后面跟條件1. 比較運(yùn)算符：= > < >= <= <> !=

2. between 80 and 100值在80到100之間3. in(80,90,100) 值是80或90或1004. like 'egon%'pattern可以是%或_，%表示任意多字符

_表示一個(gè)字符5. 邏輯運(yùn)算符：在多個(gè)條件直接可以使用邏輯運(yùn)算符 and or not

單條件查詢

SELECT name FROM employee WHERE post='sale';#注意優(yōu)先級(jí),where的優(yōu)先級(jí)比select要高,所以順序是先找到這個(gè)employee表,然后按照post='sale'的條件,然后去表里面select數(shù)據(jù)

多條件查詢

SELECT name,salary FROM employee WHERE post='teacher' AND salary>10000;

關(guān)鍵字BETWEEN AND 寫的是一個(gè)區(qū)間

#就是salary>=10000 and salary<=20000的數(shù)據(jù)

SELECT name,salary FROM employee WHERE salary BETWEEN 10000 AND 20000;#加個(gè)not,就是不在這個(gè)區(qū)間內(nèi),薪資小于10000的或者薪資大于20000的,注意沒有等于

SELECT name,salary FROM employee WHERE salary NOT BETWEEN 10000 AND 20000;

關(guān)鍵字IS NULL(判斷某個(gè)字段是否為NULL不能用等號(hào)，需要用IS) 判斷null只能用is

SELECT name,post_comment FROM employee WHERE post_comment IS NULL;#IS NOT NULL不等于NULL

ELECT name,post_comment FROM employee WHERE post_comment IS NOT NULL;#注意''是空字符串,不是null,兩個(gè)是不同的東西,null是啥也沒有,''是空的字符串的意思,是一種數(shù)據(jù)類型,null是另外一種數(shù)據(jù)類型

SELECT name,post_comment FROM employee WHERE post_comment='';

關(guān)鍵字IN集合查詢

SELECT name,salary FROM employee WHERE salary=3000 OR salary=3500 OR salary=4000 OR salary=9000;#寫太麻煩了,寫一大堆的or,下面用in這個(gè)簡(jiǎn)單的寫法來搞

SELECT name,salary FROM employee WHERE salary IN (3000,3500,4000,9000) ;

SELECT name,salary FROM employee WHERE salary NOT IN (3000,3500,4000,9000);

關(guān)鍵字LIKE模糊查詢,模糊匹配,可以結(jié)合通配符來使用

通配符’%’ #匹配任意所有字符

SELECT * FROM employee WHERE name LIKE 'eg%';

通配符’_’#匹配任意一個(gè)字符

SELECT * FROM employee WHERE name LIKE 'al__';#注意我這里寫的兩個(gè)_,用1個(gè)的話,匹配不到alex,因?yàn)閍l后面還有兩個(gè)字符ex

select id,name,agefrom employee where id>7;

首先先找到employee表,找到這個(gè)表之后,mysql會(huì)拿著where后面的約束條件去表里面找符合條件的數(shù)據(jù),然后遍歷你表中所有的數(shù)據(jù),查看一下id是否大于7,逐條的對(duì)比,然后只要發(fā)現(xiàn)id比7大的,它就會(huì)把這一整條記錄給select,但是select說我只拿id、name、age這個(gè)三個(gè)字段里面的數(shù)據(jù),然后就打印了這三個(gè)字段的數(shù)據(jù),然后where繼續(xù)往下過濾,看看id是不是還有大于7的,然后發(fā)現(xiàn)一個(gè)符合條件的就給select一個(gè),然后重復(fù)這樣的事情,直到把數(shù)據(jù)全部過濾一遍才會(huì)結(jié)束.這就是where條件的一個(gè)工作方式

GROUP BY: 分組查詢

分組指的是: 將所有記錄按照某個(gè)相同字段進(jìn)行歸類,比如針對(duì)員工信息表的職位分組,或者按照性別進(jìn)行分組等,分組發(fā)生在where之后,即分組是基于where之后得到的記錄而進(jìn)行的

SELECT post FROM employee GROUP BY post;

注意: 我們按照post字段分組,那么select查詢的字段只能是post,想要獲取組內(nèi)的其他相關(guān)信息,需要借助函數(shù)

GROUP BY關(guān)鍵字和GROUP_CONCAT()函數(shù)一起使用,按部門分組,每個(gè)組有哪些員工,都顯示出來

#按照崗位分組,并查看組內(nèi)所有成員名,通過逗號(hào)拼接在一起

SELECT post,GROUP_CONCAT(name)FROM employee GROUP BY post;

SELECT post,GROUP_CONCAT(name,':',salary) as emp_members FROM employee GROUP BY post;

GROUP BY一般都會(huì)與聚合函數(shù)一起使用,聚合是什么意思: 聚合就是將分組的數(shù)據(jù)聚集到一起,合并起來,拿到一個(gè)最后的結(jié)果

#按照崗位分組,并查看每個(gè)組有多少人,每個(gè)人都有唯一的id號(hào),我count是計(jì)算一下分組之后每組有多少的id記錄,通過這個(gè)id記錄我就知道每個(gè)組有多少人了

select post,count(id) as count from employee group by post;

關(guān)于集合函數(shù),mysql提供了以下幾種聚合函數(shù): count、max、min、avg、sum等,上面的group_concat也算是一個(gè)聚合函數(shù)了,做字符串拼接的操作

注意:

如果我們用設(shè)置了unique約束的字段作為分組的依據(jù)，則每一條記錄自成一組，這種分組沒有意義

多條記錄之間的某個(gè)字段值相同，該字段通常用來作為分組的依據(jù)

聚合函數(shù)

強(qiáng)調(diào): 聚合函數(shù)聚合的是組的內(nèi)容,若是沒有分組,則默認(rèn)一組

示例:#count是統(tǒng)計(jì)個(gè)數(shù)用的

SELECT COUNT(*) FROM employee;#后面跟where條件的意思是統(tǒng)計(jì)一下滿足depart_id=1這個(gè)的所有記錄的個(gè)數(shù)

SELECT COUNT(*) FROM employee WHERE depart_id=1;#max()統(tǒng)計(jì)分組后每組的最大值,這里沒有寫group by,那么就是統(tǒng)計(jì)整個(gè)表中所有記錄中薪資最大的,薪資的值

SELECT MAX(salary) FROM employee;

SELECT MIN(salary) FROM employee;

SELECT AVG(salary) FROM employee;

SELECT SUM(salary) FROM employee;

SELECT SUM(salary) FROM employee WHERE depart_id=3;

HAVING

having的語(yǔ)法格式和where是一模一樣的,只不過having是在分組之后進(jìn)行的進(jìn)一步的過濾,where不能使用聚合函數(shù),having是可以使用聚合函數(shù)的

執(zhí)行優(yōu)先級(jí)從高到低：where > group by > having

1. Where 發(fā)生在分組group by之前,因而Where中可以有任意字段,但是絕對(duì)不能使用聚合函數(shù)

2. Having發(fā)生在分組groupby之后,因而Having中可以使用分組的字段,無法直接取到其他字段,having是可以使用聚合函數(shù)

統(tǒng)計(jì)各部門年齡在30歲及以上的員工的平均薪資，并且保留平均工資大于10000的部門

select post,avg(salary) as new_safrom employee where age>=30 group by post having avg(salary) > 10000;

注意: having只能在group by后面運(yùn)行

ORDER BY: 查詢排序

#默認(rèn)是升序排列

SELECT *FROM employee ORDER BY salary;#升序

SELECT *FROM employee ORDER BY salary ASC;#降序

SELECT *FROM employee ORDER BY salary DESC;#按照age來排序

SELECT *FROM employee ORDER BY age;#先按照age升序,如果年紀(jì)相同,則按照薪資降序

SELECT * fromemployee ORDER BY age,salary DESC;#注意排序的條件用逗號(hào)分隔

LIMIT: 限制查詢的記錄數(shù)

#取出工資最高的前三位,默認(rèn)初始位置為0,從第一條開始順序取出三條

SELECT * FROM employee ORDER BY salary DESC LIMIT 3;#從第0開始,即先查詢出第一條,然后包含這一條在內(nèi)往后查5條

SELECT * FROM employee ORDER BY salary DESC LIMIT 0,5;#從第5開始,即先查詢出第6條,然后包含這一條在內(nèi)往后查5條

SELECT * FROM employee ORDER BY salary DESC LIMIT 5,5;

正則表達(dá)式查詢

之前用like做模糊匹配,只有%和_，局限性比較強(qiáng),所以用正則匹配

SELECT * FROM employee WHERE name REGEXP '^ale';

SELECT* FROM employee WHERE name REGEXP 'on$';

SELECT* FROM employee WHERE name REGEXP 'm{2}';

小結(jié): 對(duì)字符串匹配的方式

WHERE name = 'egon';

WHERE name LIKE 'yua%';

WHERE name REGEXP 'on$';

總結(jié)

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