目錄
1.單表查詢的語法
SELECT 字段1,字段2... FROM 表名
WHERE 條件
GROUP BY field
HAVING 篩選
ORDER BY field
LIMIT 限制條數
2.關鍵字的執行優先級(重點)
重點中的重點：關鍵字的執行優先級
from
where
group by
having
select
distinct
order by
limit
1.找到表:from
2.拿着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
3.簡單查詢
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 employee(
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 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
准備表和記錄
# 簡單查詢
SELECT id,name,sex,age,hire_date,post,post_comment,salary,office,depart_id
FROM employee;
SELECT * FROM employee;
SELECT name,salary FROM employee;
# 避免重復DISTINCT
SELECT DISTINCT post FROM employee;
# 通過四則運算查詢
SELECT name, salary*12 FROM employee;
SELECT name, salary*12 AS Annual_salary FROM employee;
SELECT name, salary*12 Annual_salary FROM employee;
# 定義顯示格式
CONCAT() 函數用於連接字符串
SELECT CONCAT('姓名: ',name,' 年薪: ', salary*12) AS Annual_salary
FROM employee;
CONCAT_WS() 第一個參數為分隔符
SELECT CONCAT_WS(':',name,salary*12) AS Annual_salary
FROM employee;
結合CASE語句：
SELECT
(
CASE
WHEN NAME = 'egon' THEN
NAME
WHEN NAME = 'alex' THEN
CONCAT(name,'_BIGSB')
ELSE
concat(NAME, 'SB')
END
) as new_name
FROM
emp;
小練習：
1 查出所有員工的名字，薪資,格式為
<名字:egon> <薪資:3000>
2 查出所有的崗位（去掉重復）
3 查出所有員工名字，以及他們的年薪,年薪的字段名為annual_year
select concat('<名字:',name,'> ','<薪資:',salary,'>') from employee;
select distinct depart_id from employee;
select name,salary*12 annual_salary from employee;
4.WHERE約束
where字句中可以使用：
1.比較運算符：> < >= <= <> !=
- between 80 and 100 值在10到20之間
- in(80,90,100) 值是10或20或30
4.like 'egon%'
pattern可以是%或_，
%表示任意多字符
_表示一個字符
5.邏輯運算符：在多個條件直接可以使用邏輯運算符 and or not
# 1:單條件查詢
SELECT name FROM employee
WHERE post='sale';
# 2:多條件查詢
SELECT name,salary FROM employee
WHERE post='teacher' AND salary>10000;
# 3:關鍵字BETWEEN AND
SELECT name,salary FROM employee
WHERE salary BETWEEN 10000 AND 20000;
SELECT name,salary FROM employee
WHERE salary NOT BETWEEN 10000 AND 20000;
# 4:關鍵字IS NULL(判斷某個字段是否為NULL不能用等號，需要用IS)
SELECT name,post_comment FROM employee
WHERE post_comment IS NULL;
SELECT name,post_comment FROM employee
WHERE post_comment IS NOT NULL;
SELECT name,post_comment FROM employee
WHERE post_comment=''; 注意''是空字符串，不是null
ps：
執行
update employee set post_comment='' where id=2;
再用上條查看，就會有結果了
# 5:關鍵字IN集合查詢
SELECT name,salary FROM employee
WHERE salary=3000 OR salary=3500 OR salary=4000 OR salary=9000 ;
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) ;
# 6:關鍵字LIKE模糊查詢
通配符’%’
SELECT * FROM employee
WHERE name LIKE 'eg%';
通配符’_’
SELECT * FROM employee
WHERE name LIKE 'al__';
小練習：
1. 查看崗位是teacher的員工姓名、年齡
2. 查看崗位是teacher且年齡大於30歲的員工姓名、年齡
3. 查看崗位是teacher且薪資在9000-1000范圍內的員工姓名、年齡、薪資
4. 查看崗位描述不為NULL的員工信息
5. 查看崗位是teacher且薪資是10000或9000或30000的員工姓名、年齡、薪資
6. 查看崗位是teacher且薪資不是10000或9000或30000的員工姓名、年齡、薪資
7. 查看崗位是teacher且名字是jin開頭的員工姓名、年薪
select name,age from employee where post = 'teacher';
select name,age from employee where post='teacher' and age > 30;
select name,age,salary from employee where post='teacher' and salary between 9000 and 10000;
select * from employee where post_comment is not null;
select name,age,salary from employee where post='teacher' and salary in (10000,9000,30000);
select name,age,salary from employee where post='teacher' and salary not in (10000,9000,30000);
select name,salary*12 from employee where post='teacher' and name like 'jin%';
5.分組查詢:GROUP BY
5.1什么是分組？為什么要分組？
# 1、首先明確一點：分組發生在where之后，即分組是基於where之后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’這個字后面的字段，就是我們分組的依據
# 4、大前提：
可以按照任意字段分組，但是分組完畢后，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
5.2ONLY_FULL_GROUP_BY
#查看MySQL 5.7默認的sql_mode如下：
mysql> select @@global.sql_mode;
ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
#！！！注意
ONLY_FULL_GROUP_BY的語義就是確定select target list中的所有列的值都是明確語義，簡單的說來，在ONLY_FULL_GROUP_BY模式下，target list中的值要么是來自於聚集函數的結果，要么是來自於group by list中的表達式的值。
#設置sql_mole如下操作(我們可以去掉ONLY_FULL_GROUP_BY模式)：
mysql> set global sql_mode='STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION';
5.3！！！SQL_MODE設置！！！
mysql> select @@global.sql_mode;
+-------------------+
| @@global.sql_mode |
+-------------------+
| |
+-------------------+
1 row in set (0.00 sec)
mysql> select * from emp group by post;
+----+------+--------+-----+------------+----------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------+--------+-----+------------+----------------------------+--------------+------------+--------+-----------+
| 14 | 張野 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 9 | 歪歪 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 1 | egon | male | 18 | 2017-03-01 | 老男孩駐沙河辦事處外交大使 | NULL | 7300.33 | 401 | 1 |
+----+------+--------+-----+------------+----------------------------+--------------+------------+--------+-----------+
4 rows in set (0.00 sec)
#由於沒有設置ONLY_FULL_GROUP_BY,於是也可以有結果，默認都是組內的第一條記錄，但其實這是沒有意義的
mysql> set global sql_mode='ONLY_FULL_GROUP_BY';
Query OK, 0 rows affected (0.00 sec)
mysql> quit #設置成功后，一定要退出，然后重新登錄方可生效
Bye
mysql> use db1;
Database changed
mysql> select * from emp group by post; #報錯
ERROR 1055 (42000): 'db1.emp.id' isn't in GROUP BY
mysql> select post,count(id) from emp group by post; #只能查看分組依據和使用聚合函數
+----------------------------+-----------+
| post | count(id) |
+----------------------------+-----------+
| operation | 5 |
| sale | 5 |
| teacher | 7 |
| 老男孩駐沙河辦事處外交大使 | 1 |
+----------------------------+-----------+
4 rows in set (0.00 sec)
5.4GROUP BYv
單獨使用GROUP BY關鍵字分組
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，想要獲取組內的其他相關信息，需要借助函數
GROUP BY關鍵字和GROUP_CONCAT()函數一起使用
SELECT post,GROUP_CONCAT(name) FROM employee GROUP BY post;#按照崗位分組，並查看組內成員名
SELECT post,GROUP_CONCAT(name) as emp_members FROM employee GROUP BY post;
GROUP BY與聚合函數一起使用
select post,count(id) as count from employee group by post;#按照崗位分組，並查看每個組有多少人
強調：
如果我們用unique的字段作為分組的依據，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字段值相同，該字段通常用來作為分組的依據
5.5聚合函數
# 強調：聚合函數聚合的是組的內容，若是沒有分組，則默認一組
示例：
SELECT COUNT(*) FROM employee;
SELECT COUNT(*) FROM employee WHERE depart_id=1;
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;
5.6小練習:
1. 查詢崗位名以及崗位包含的所有員工名字
2. 查詢崗位名以及各崗位內包含的員工個數
3. 查詢公司內男員工和女員工的個數
4. 查詢崗位名以及各崗位的平均薪資
5. 查詢崗位名以及各崗位的最高薪資
6. 查詢崗位名以及各崗位的最低薪資
7. 查詢男員工與男員工的平均薪資，女員工與女員工的平均薪資
# 題1：分組
mysql> select post,group_concat(name) from employee group by post;
+-----------------------------------------+---------------------------------------------------------+
| post | group_concat(name) |
+-----------------------------------------+---------------------------------------------------------+
| operation | 張野,程咬金,程咬銀,程咬銅,程咬鐵 |
| sale | 歪歪,丫丫,丁丁,星星,格格 |
| teacher | alex,wupeiqi,yuanhao,liwenzhou,jingliyang,jinxin,成龍 |
| 老男孩駐沙河辦事處外交大使 | egon |
+-----------------------------------------+---------------------------------------------------------+
# 題目2：
mysql> select post,count(id) from employee group by post;
+-----------------------------------------+-----------+
| post | count(id) |
+-----------------------------------------+-----------+
| operation | 5 |
| sale | 5 |
| teacher | 7 |
| 老男孩駐沙河辦事處外交大使 | 1 |
+-----------------------------------------+-----------+
# 題目3：
mysql> select sex,count(id) from employee group by sex;
+--------+-----------+
| sex | count(id) |
+--------+-----------+
| male | 10 |
| female | 8 |
+--------+-----------+
# 題目4：
mysql> select post,avg(salary) from employee group by post;
+-----------------------------------------+---------------+
| post | avg(salary) |
+-----------------------------------------+---------------+
| operation | 16800.026000 |
| sale | 2600.294000 |
| teacher | 151842.901429 |
| 老男孩駐沙河辦事處外交大使 | 7300.330000 |
+-----------------------------------------+---------------+
# 題目5
mysql> select post,max(salary) from employee group by post;
+-----------------------------------------+-------------+
| post | max(salary) |
+-----------------------------------------+-------------+
| operation | 20000.00 |
| sale | 4000.33 |
| teacher | 1000000.31 |
| 老男孩駐沙河辦事處外交大使 | 7300.33 |
+-----------------------------------------+-------------+
# 題目6
mysql> select post,min(salary) from employee group by post;
+-----------------------------------------+-------------+
| post | min(salary) |
+-----------------------------------------+-------------+
| operation | 10000.13 |
| sale | 1000.37 |
| teacher | 2100.00 |
| 老男孩駐沙河辦事處外交大使 | 7300.33 |
+-----------------------------------------+-------------+
# 題目七
mysql> select sex,avg(salary) from employee group by sex;
+--------+---------------+
| sex | avg(salary) |
+--------+---------------+
| male | 110920.077000 |
| female | 7250.183750 |
+--------+---------------+
6.HAVING過濾
HAVING與WHERE不一樣的地方在於!!!!!!
# ！！！執行優先級從高到低：where > group by > having
# 1. Where 發生在分組group by之前，因而Where中可以有任意字段，但是絕對不能使用聚合函數。
# 2. Having發生在分組group by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,可以使用聚合函數
mysql> select @@sql_mode;
+--------------------+
| @@sql_mode |
+--------------------+
| ONLY_FULL_GROUP_BY |
+--------------------+
1 row in set (0.00 sec)
mysql> select * from emp where salary > 100000;
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
1 row in set (0.00 sec)
mysql> select * from emp having salary > 100000;
ERROR 1463 (42000): Non-grouping field 'salary' is used in HAVING clause
mysql> select post,group_concat(name) from emp group by post having salary > 10000;#錯誤，分組后無法直接取到salary字段
ERROR 1054 (42S22): Unknown column 'salary' in 'having clause'
mysql> select post,group_concat(name) from emp group by post having avg(salary) > 10000;
+-----------+-------------------------------------------------------+
| post | group_concat(name) |
+-----------+-------------------------------------------------------+
| operation | 程咬鐵,程咬銅,程咬銀,程咬金,張野 |
| teacher | 成龍,jinxin,jingliyang,liwenzhou,yuanhao,wupeiqi,alex |
+-----------+-------------------------------------------------------+
2 rows in set (0.00 sec)[](javascript:void(0);
小練習：
1. 查詢各崗位內包含的員工個數小於2的崗位名、崗位內包含員工名字、個數
3. 查詢各崗位平均薪資大於10000的崗位名、平均工資
4. 查詢各崗位平均薪資大於10000且小於20000的崗位名、平均工資
# 題1：
mysql> select post,group_concat(name),count(id) from employee group by post having count(id) < 2;
+-----------------------------------------+--------------------+-----------+
| post | group_concat(name) | count(id) |
+-----------------------------------------+--------------------+-----------+
| 老男孩駐沙河辦事處外交大使 | egon | 1 |
+-----------------------------------------+--------------------+-----------+
# 題目2：
mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000;
+-----------+---------------+
| post | avg(salary) |
+-----------+---------------+
| operation | 16800.026000 |
| teacher | 151842.901429 |
+-----------+---------------+
# 題目3：
mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000 and avg(salary) <20000;
+-----------+--------------+
| post | avg(salary) |
+-----------+--------------+
| operation | 16800.026000 |
+-----------+--------------+
7.查詢排序:ORDER BY
按單列排序
SELECT * FROM employee ORDER BY salary;
SELECT * FROM employee ORDER BY salary ASC;
SELECT * FROM employee ORDER BY salary DESC;
按多列排序:先按照age排序，如果年紀相同，則按照薪資排序
SELECT * from employee
ORDER BY age,
salary DESC;
小練習：
1. 查詢所有員工信息，先按照age升序排序，如果age相同則按照hire_date降序排序
2. 查詢各崗位平均薪資大於10000的崗位名、平均工資,結果按平均薪資升序排列
3. 查詢各崗位平均薪資大於10000的崗位名、平均工資,結果按平均薪資降序排列
# 題目1
mysql> select * from employee ORDER BY age asc,hire_date desc;
# 題目2
mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000 order by avg(salary) asc;
+-----------+---------------+
| post | avg(salary) |
+-----------+---------------+
| operation | 16800.026000 |
| teacher | 151842.901429 |
+-----------+---------------+
# 題目3
mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000 order by avg(salary) desc;
+-----------+---------------+
| post | avg(salary) |
+-----------+---------------+
| teacher | 151842.901429 |
| operation | 16800.026000 |
+-----------+---------------+
8.限制查詢的記錄數:LIMIT
示例：
SELECT * FROM employee ORDER BY salary DESC
LIMIT 3; #默認初始位置為0
SELECT * FROM employee ORDER BY salary DESC
LIMIT 0,5; #從第0開始，即先查詢出第一條，然后包含這一條在內往后查5條
SELECT * FROM employee ORDER BY salary DESC
LIMIT 5,5; #從第5開始，即先查詢出第6條，然后包含這一條在內往后查5條
小練習：
1. 分頁顯示，每頁5條
mysql> select * from employee limit 0,5;
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| 1 | egon | male | 18 | 2017-03-01 | 老男孩駐沙河辦事處外交大使 | NULL | 7300.33 | 401 | 1 |
| 2 | alex | male | 78 | 2015-03-02 | teacher | | 1000000.31 | 401 | 1 |
| 3 | wupeiqi | male | 81 | 2013-03-05 | teacher | NULL | 8300.00 | 401 | 1 |
| 4 | yuanhao | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 |
| 5 | liwenzhou | male | 28 | 2012-11-01 | teacher | NULL | 2100.00 | 401 | 1 |
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
5 rows in set (0.00 sec)
mysql> select * from employee limit 5,5;
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
| 6 | jingliyang | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
| 7 | jinxin | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
| 8 | 成龍 | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 |
| 9 | 歪歪 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 10 | 丫丫 | female | 38 | 2010-11-01 | sale | NULL | 2000.35 | 402 | 2 |
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
5 rows in set (0.00 sec)
mysql> select * from employee limit 10,5;
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| 11 | 丁丁 | female | 18 | 2011-03-12 | sale | NULL | 1000.37 | 402 | 2 |
| 12 | 星星 | female | 18 | 2016-05-13 | sale | NULL | 3000.29 | 402 | 2 |
| 13 | 格格 | female | 28 | 2017-01-27 | sale | NULL | 4000.33 | 402 | 2 |
| 14 | 張野 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 15 | 程咬金 | male | 18 | 1997-03-12 | operation | NULL | 20000.00 | 403 | 3 |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
5 rows in set (0.00 sec)
9.使用正則表達式查詢
SELECT * FROM employee WHERE name REGEXP '^ale';
SELECT * FROM employee WHERE name REGEXP 'on$';
SELECT * FROM employee WHERE name REGEXP 'm{2}';
小結：對字符串匹配的方式
WHERE name = 'egon';
WHERE name LIKE 'yua%';
WHERE name REGEXP 'on$';
小練習：
查看所有員工中名字是jin開頭，n或者g結果的員工信息
select * from employee where name regexp '^jin.*[gn]$';