MySql單表查詢

@[TOC]

1. 單表查詢語法

select distinct 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(shù)

2. 關(guān)鍵字執(zhí)行的優(yōu)先級(jí)

from
where
group by
select
distinct
having
order by
limit

1.找到表:from

2.拿著where指定的約束條件煎饼，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多糠，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 by

7.限制結(jié)果的顯示條數(shù)

3. 簡單查詢

建表

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(hào)     depart_id           int



#創(chuàng)建表
create table employee(
id int not null unique auto_increment,
emp_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(gè)部門一個(gè)屋子
depart_id int
);


#查看表結(jié)構(gòu)
mysql> desc employee;
+--------------+-----------------------+------+-----+---------+----------------+
| Field        | Type                  | Null | Key | Default | Extra          |
+--------------+-----------------------+------+-----+---------+----------------+
| id           | int(11)               | NO   | PRI | NULL    | auto_increment |
| emp_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(gè)部門：教學(xué)等曼，銷售，運(yùn)營
insert into employee(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(xué)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(yùn)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(tǒng)中，插入中文字符惊楼，select的結(jié)果為空白狰右，可以將所有字符編碼統(tǒng)一設(shè)置成gbk

準(zhǔn)備表和記錄

建表和數(shù)據(jù)準(zhǔn)備

查詢

#簡單查詢
    SELECT id,emp_name,sex,age,hire_date,post,post_comment,salary,office,depart_id 
    FROM employee;

    SELECT * FROM employee;

    SELECT emp_name,salary FROM employee;

#避免重復(fù)DISTINCT
    SELECT DISTINCT post FROM employee;    

#通過四則運(yùn)算查詢
    SELECT emp_name, salary*12 FROM employee;
    SELECT emp_name, salary*12 AS Annual_salary FROM employee;
    SELECT emp_name, salary*12 Annual_salary FROM employee;

#定義顯示格式
   CONCAT() 函數(shù)用于連接字符串
   SELECT CONCAT('姓名: ',emp_name,'  年薪: ', salary*12)  AS Annual_salary 
   FROM employee;
   
   CONCAT_WS() 第一個(gè)參數(shù)為分隔符
   SELECT CONCAT_WS(':',emp_name,salary*12)  AS Annual_salary 
   FROM employee;

   結(jié)合CASE語句：
   SELECT
       (
           CASE
           WHEN emp_name = 'jingliyang' THEN
               emp_name
           WHEN emp_name = 'alex' THEN
               CONCAT(emp_name,'_BIGSB')
           ELSE
               concat(emp_name, 'SB')
           END
       ) as new_name
   FROM
       employee;

練習(xí):
1 查出所有員工的名字杰捂，薪資,格式為
<名字:egon> <薪資:3000>
2 查出所有的崗位（去掉重復(fù)）
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:',emp_name,'>    ','<薪資:',salary,'>') from employee;
select distinct depart_id from employee;
select emp_name,salary*12 annual_salary from employee;

4. where約束

where字句中可以使用：

比較運(yùn)算符：> < >= <= <> !=
between 80 and 100 值在80到100之間
in(80,90,100) 值是80或90或100
like 'e%'
通配符可以是%或_棋蚌，
%表示任意多字符
_表示一個(gè)字符
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

#1:單條件查詢
    SELECT emp_name FROM employee
        WHERE post='sale';
        
#2:多條件查詢
    SELECT emp_name,salary FROM employee
        WHERE post='teacher' AND salary>10000;

#3:關(guān)鍵字BETWEEN AND
    SELECT emp_name,salary FROM employee 
        WHERE salary BETWEEN 10000 AND 20000;

    SELECT emp_name,salary FROM employee 
        WHERE salary NOT BETWEEN 10000 AND 20000;
    
#4:關(guān)鍵字IS NULL(判斷某個(gè)字段是否為NULL不能用等號(hào)嫁佳，需要用IS)
    SELECT emp_name,post_comment FROM employee 
        WHERE post_comment IS NULL;

    SELECT emp_name,post_comment FROM employee 
        WHERE post_comment IS NOT NULL;
        
    SELECT emp_name,post_comment FROM employee 
        WHERE post_comment=''; 注意''是空字符串，不是null
    ps：
        執(zhí)行
        update employee set post_comment='' where id=2;
        再用上條查看谷暮，就會(huì)有結(jié)果了

#5:關(guān)鍵字IN集合查詢
    SELECT emp_name,salary FROM employee 
        WHERE salary=3000 OR salary=3500 OR salary=4000 OR salary=9000 ;
    
    SELECT emp_name,salary FROM employee 
        WHERE salary IN (3000,3500,4000,9000) ;

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

#6:關(guān)鍵字LIKE模糊查詢
    通配符’%’
    SELECT * FROM employee 
            WHERE emp_name LIKE 'eg%';

    通配符’_’
    SELECT * FROM employee 
            WHERE emp_name LIKE 'al__';

練習(xí):

1. 查看崗位是teacher的員工姓名蒿往、年齡
2. 查看崗位是teacher且年齡大于30歲的員工姓名、年齡
3. 查看崗位是teacher且薪資在9000-10000范圍內(nèi)的員工姓名湿弦、年齡瓤漏、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、年齡颊埃、薪資
6. 查看崗位是teacher且薪資不是10000或9000或30000的員工姓名蔬充、年齡、薪資
7. 查看崗位是teacher且名字是jin開頭的員工姓名班利、年薪

select emp_name,age from employee where post = 'teacher';
select emp_name,age from employee where post='teacher' and age > 30; 
select emp_name,age,salary from employee where post='teacher' and salary between 9000 and 10000;
select * from employee where post_comment is not null;
select emp_name,age,salary from employee where post='teacher' and salary in (10000,9000,30000);
select emp_name,age,salary from employee where post='teacher' and salary not in (10000,9000,30000);
select emp_name,salary*12 from employee where post='teacher' and emp_name like 'jin%';

5. group by

單獨(dú)使用GROUP BY關(guān)鍵字分組
SELECT post FROM employee GROUP BY post;
注意：我們按照post字段分組饥漫，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)信息罗标，需要借助函數(shù)

GROUP BY關(guān)鍵字和GROUP_CONCAT()函數(shù)一起使用
SELECT post,GROUP_CONCAT(emp_name) FROM employee GROUP BY post;#按照崗位分組庸队，并查看組內(nèi)成員名
SELECT post,GROUP_CONCAT(emp_name) as emp_members FROM employee GROUP BY post;

GROUP BY與聚合函數(shù)一起使用
select post,count(id) as count from employee group by post;#按照崗位分組，并查看每個(gè)組有多少人
強(qiáng)調(diào):
如果我們用unique的字段作為分組的依據(jù)闯割，則每一條記錄自成一組彻消，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)

6.聚合函數(shù)

強(qiáng)調(diào)：聚合函數(shù)聚合的是組的內(nèi)容宙拉，若是沒有分組证膨，則默認(rèn)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;

練習(xí):

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(nèi)包含的員工個(gè)數(shù)
3. 查詢公司內(nèi)男員工和女員工的個(gè)數(shù)
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

答案:

#題1：分組
mysql> select post,group_concat(emp_name) from employee group by post;
+-----------------------------------------+---------------------------------------------------------+
| post                                    | group_concat(emp_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 |
+--------+---------------+

答案

7. HAVING過濾

HAVING與WHERE不一樣的地方在于!!!!!!

#９那Ｑ肜铡！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之前澳化，因而Where中可以有任意字段崔步，但是絕對(duì)不能使用聚合函數(shù)。
#2. Having發(fā)生在分組group by之后缎谷，因而Having中可以使用分組的字段井濒，無法直接取到其他字段,可以使用聚合函數(shù)

mysql> select @@sql_mode;
+--------------------+
| @@sql_mode         |
+--------------------+
| ONLY_FULL_GROUP_BY |
+--------------------+
row in set (0.00 sec)

mysql> select * from emp where salary > 100000;
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
| id | emp_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 |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
row in set (0.00 sec)

mysql> select post,group_concat(emp_name) from emp group by post having salary > 10000;#錯(cuò)誤灶似，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(emp_name) from emp group by post having avg(salary) > 10000;
+-----------+-------------------------------------------------------+
| post | group_concat(emp_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 |
+-----------+-------------------------------------------------------+
rows in set (0.00 sec)

 驗(yàn)證

練習(xí):

1. 查詢各崗位內(nèi)包含的員工個(gè)數(shù)小于2的崗位名、崗位內(nèi)包含員工名字瑞你、個(gè)數(shù)
3. 查詢各崗位平均薪資大于10000的崗位名酪惭、平均工資
4. 查詢各崗位平均薪資大于10000且小于20000的崗位名、平均工資

#題1：
mysql> select post,group_concat(emp_name),count(id) from employee group by post having count(id) < 2;
+-----------------------------------------+--------------------+-----------+
| post                                    | group_concat(emp_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 |
+-----------+--------------+

答案

8. ORDER BY 查詢排序

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排序者甲，如果年紀(jì)相同春感，則按照薪資排序
    SELECT * from employee
        ORDER BY age,
        salary DESC;

練習(xí):

1. 查詢所有員工信息，先按照age升序排序虏缸，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于10000的崗位名鲫懒、平均工資,結(jié)果按平均薪資升序排列
3. 查詢各崗位平均薪資大于10000的崗位名、平均工資,結(jié)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 |
+-----------+---------------+

答案

9. limit 限制查詢的記錄數(shù)

示例：
    SELECT * FROM employee ORDER BY salary DESC 
        LIMIT 3;                    #默認(rèn)初始位置為0 
    
    SELECT * FROM employee ORDER BY salary DESC
        LIMIT 0,5; #從第0開始刽辙，即先查詢出第一條窥岩，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; #從第5開始，即先查詢出第6條宰缤，然后包含這一條在內(nèi)往后查5條

練習(xí):

1. 分頁顯示颂翼，每頁5條

mysql> select * from  employee limit 0,5;
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| id | emp_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 |
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
rows in set (0.00 sec)

mysql> select * from  employee limit 5,5;
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
| id | emp_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 |
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
rows in set (0.00 sec)

mysql> select * from  employee limit 10,5;
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| id | emp_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 |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
rows in set (0.00 sec)

答案

10. 使用正則表達(dá)式查詢

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

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

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


小結(jié)：對(duì)字符串匹配的方式
WHERE emp_name = 'egon';
WHERE emp_name LIKE 'yua%';
WHERE emp_name REGEXP 'on$';

練習(xí):
查看所有員工中名字是jin開頭，n或者g結(jié)果的員工信息

select * from employee where emp_name regexp '^jin.*[gn]$';

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MySql單表查詢

1. 單表查詢語法

2. 關(guān)鍵字執(zhí)行的優(yōu)先級(jí)

3. 簡單查詢

4. where約束

5. group by

6.聚合函數(shù)

7. HAVING過濾

8. ORDER BY 查詢排序

9. limit 限制查詢的記錄數(shù)

10. 使用正則表達(dá)式查詢

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