數據庫之單表查詢
阿新 • • 發佈：2018-05-13
年齡 tween 員工 分頁 lar 取出 arc windows mit
select * from emp where name regexp ‘^jin.*(n|g)$‘;
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行分組group by，如果沒有group by，則整體作為一組 4.將分組的結果進行having過濾 5.執行select 6.去重 7.將結果按條件排序：order by 8.限制結果的顯示條數 詳細：http://www.cnblogs.com/linhaifeng/articles/7372774.html
準備表和記錄 company.employee 員工id id int 姓名 emp_name varchar 性別 sex enum 年齡 age int 入職日期 hire_date date 崗位 post varchar 職位描述 post_comment varchar 薪水 salary double 辦公室 office int 部門編號 depart_id int#創建表 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 );#查看表結構 mysql> desc employee; +--------------+-----------------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +--------------+-----------------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | name | varchar(20) | NO | | NULL | | | sex | enum(‘male‘,‘female‘) | NO | | male | | | age | int(3) unsigned | NO | | 28 | | | hire_date | date | NO | | NULL | | | post | varchar(50) | YES | | NULL | | | post_comment | varchar(100) | YES | | NULL | | | salary | double(15,2) | YES | | NULL | | | office | int(11) | YES | | NULL | | | depart_id | int(11) | YES | | NULL | | +--------------+-----------------------+------+-----+---------+----------------+ #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 (‘egon‘,‘male‘,18,‘20170301‘,‘老男孩駐沙河辦事處外交大使‘,7300.33,401,1), #以下是教學部 (‘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：如果在windows系統中，插入中文字符，select的結果為空白，可以將所有字符編碼統一設置成gbk
小練習： select id,name from db39.emp where id >= 3 and id <= 6； select * from db39.emp where id between 3 and 6; select * from emp where salary = 20000 or salary = 18000 or salary = 17000; select * from emp where salary in (20000,18000,17000); 要求：查詢員工姓名中包含i字母的員工姓名與其薪資 select name,salary from db39.emp where name like ‘%i%‘ 要求：查詢員工姓名是由四個字符組成的的員工姓名與其薪資 select name,salary from db39.emp where name like ‘____‘; select name,salary from db39.emp where char_length(name) = 4; select * from db39.emp where id not between 3 and 6; select * from emp where salary not in (20000,18000,17000); 要求：查詢崗位描述為空的員工名與崗位名 select name,post from db39.emp where post_comment is NULL; select name,post from db39.emp where post_comment is not NULL;
一 什麽是分組？為什麽要分組？ #1、首先明確一點：分組發生在where之後，即分組是基於where之後得到的記錄而進行的 #2、分組指的是：將所有記錄按照某個相同字段進行歸類，比如針對員工信息表的職位分組，或者按照性別進行分組等 #3、為何要分組呢？ 取每個部門的最高工資 取每個部門的員工數 取男人數和女人數 小竅門：‘每’這個字後面的字段，就是我們分組的依據 #4、大前提： 可以按照任意字段分組，但是分組完畢後，比如group by post，只能查看post字段，如果想查看組內信息，需要借助於聚合函數 二，only_full_group_by （聚合函數） 三，group by #設置sql_mode為only_full_group_by，意味著以後但凡分組，只能取到分組的依據默認 mysql> set global sql_mode="strict_trans_tables,only_full_group_by"; #每個部門的最高工資 select post,max(salary) from emp group by post; select post,min(salary) from emp group by post; select post,avg(salary) from emp group by post; select post,sum(salary) from emp group by post; select post,count(id) from emp group by post;
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;
select name as 姓名,salary as 薪資 from emp; mysql> select emp.id,emp.name from emp as t1; # 報錯 mysql> select t1.id,t1.name from emp as t1;
having的語法格式與where一模一樣，只不過having是在分組之後進行的進一步過濾 即where不能用聚合函數，而having是可以用聚合函數，這也是他們倆最大的區別 1、統計各部門年齡在30歲以上的員工平均工資，並且保留平均工資大於10000的部門 select post,avg(salary) from emp where age >= 30 group by post having avg(salary) > 10000; #強調：having必須在group by後面使用 select * from emp having avg(salary) > 10000;
select * from emp order by salary asc; #默認升序排 select * from emp order by salary desc; #降序排 select * from emp order by age desc; #降序排 select * from emp order by age desc,salary asc; #先按照age降序排，再按照薪資升序排 # 統計各部門年齡在10歲以上的員工平均工資，並且保留平均工資大於1000的部門， 然後對平均工資進行排序 select post,avg(salary) from emp where age > 10 group by post having avg(salary) > 1000 order by avg(salary) ;
select * from emp limit 3; select * from emp order by salary desc limit 1; # 分頁顯示 select * from emp limit 0,5; select * from emp limit 5,5;
select * from emp where name regexp ‘^jin.*(n|g)$‘;
數據庫之單表查詢