前期表準備mysql
create table emp(
id int not null unique auto_increment,
name varchar(20) not null,
sex enum('male','female') not null default 'male', #大部分是男的
age int(3) unsigned not null default 28,
hire_date date not null,
post varchar(50),
post_comment varchar(100),
salary double(15,2),
office int, #一個部門一個屋子
depart_id int
);
#插入記錄
#三個部門：教學，銷售，運營
insert into emp(name,sex,age,hire_date,post,salary,office,depart_id) values
('jason','male',18,'20170301','張江第一帥形象代言',7300.33,401,1), #如下是教學部
('egon','male',78,'20150302','teacher',1000000.31,401,1),
('kevin','male',81,'20130305','teacher',8300,401,1),
('tank','male',73,'20140701','teacher',3500,401,1),
('owen','male',28,'20121101','teacher',2100,401,1),
('jerry','female',18,'20110211','teacher',9000,401,1),
('nick','male',18,'19000301','teacher',30000,401,1),
('sean','male',48,'20101111','teacher',10000,401,1),
('歪歪','female',48,'20150311','sale',3000.13,402,2),#如下是銷售部門
('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), #如下是運營部門
('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)
;
#ps：若是在windows系統中，插入中文字符，select的結果爲空白，能夠將全部字符編碼統一設置成gbk
# 初識查詢語句
select id,name from emp where id >= 3 and id <= 6;
# 前後順序
from
where
select
# 1.查詢id大於等於3小於等於6的數據
select id,name from emp where id >= 3 and id <= 6;
select * from emp where id between 3 and 6;
# 2.查詢薪資是20000或者18000或者17000的數據
select * from emp where salary = 20000 or salary = 18000 or salary = 17000;
select * from emp where salary in (20000,18000,17000); # 簡寫
# 3.查詢員工姓名中包含o字母的員工姓名和薪資
# 在你剛開始接觸mysql查詢的時候，建議你按照查詢的優先級順序拼寫出你的sql語句
"""
先是查哪張表 from emp
再是根據什麼條件去查 where name like ‘%o%’
再是對查詢出來的數據篩選展現部分 select name,salary
"""
select name,salary from emp where name like '%o%';
# 4.查詢員工姓名是由四個字符組成的員工姓名與其薪資
select name,salary from emp where name like '____';
select name,salary from emp where char_length(name) = 4;
# 5.查詢id小於3或者大於6的數據
select * from emp where id not between 3 and 6;
# 6.查詢薪資不在20000，18000，17000範圍的數據
select * from emp where salary not in (20000,18000,17000);
# 7.查詢崗位描述爲空的員工名與崗位名 針對null不能用等號，只能用is
select name,post from emp where post_comment = NULL; # 查詢爲空！
select name,post from emp where post_comment is NULL;
select name,post from emp where post_comment is not NULL;
# 數據分組應用場景：每一個部門的平均薪資，男女比例等
# 1.按部門分組
select * from emp group by post; # 分組後取出的是每一個組的第一條數據
select id,name,sex from emp group by post; # 驗證
"""
設置sql_mode爲only_full_group_by，意味着之後但凡分組，只能取到分組的依據，
不該該在去取組裏面的單個元素的值，那樣的話分組就沒有意義了，由於不分組就是對單個元素信息的隨意獲取
"""
set global sql_mode="strict_trans_tables,only_full_group_by";
# 從新連接客戶端
select * from emp group by post; # 報錯
select id,name,sex from emp group by post; # 報錯
select post from emp group by post; # 獲取部門信息
# 強調:只要分組了，就不可以再「直接」查找到單個數據信息了，只能獲取到組名
# 2.獲取每一個部門的最高工資
# 以組爲單位統計組內數據>>>聚合查詢(彙集到一塊兒合成爲一個結果)
# 每一個部門的最高工資
select post,max(salary) from emp group by post;
# 每一個部門的最低工資
select post,min(salary) from emp group by post;
# 每一個部門的平均工資
select post,avg(salary) from emp group by post;
# 每一個部門的工資總和
select post,sum(salary) from emp group by posest;
# 每一個部門的人數
select post,count(id) from emp group by post;
# 3.查詢分組以後的部門名稱和每一個部門下全部的學生姓名
# group_concat（分組以後用）不只能夠用來顯示除分組外字段還有拼接字符串的做用
select post,group_concat(name) from emp group by post;
select post,group_concat(name,"_SB") from emp group by post;
select post,group_concat(name,": ",salary) from emp group by post;
select post,group_concat(salary) from emp group by post;
# 4.補充concat（不分組時用）拼接字符串達到更好的顯示效果 as語法使用
select name as 姓名,salary as 薪資 from emp;
select concat("NAME: ",name) as 姓名,concat("SAL: ",salary) as 薪資 from emp;
# 補充as語法 便可以給字段起別名也能夠給表起
select emp.id,emp.name from emp as t1; # 報錯 由於表名已經被你改爲了t1
select t1.id,t1.name from emp