數據庫：數據操作-單表查詢
阿新 • • 發佈：2018-07-21
ffi 沒有 成功 模糊查詢 concat_ws 範圍 chan 四則運算 family
一 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
二 關鍵字的執行優先級（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.限制結果的顯式條數
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
mysql> create table employee(
-> id int not null unique auto_increment,
-> name varchar(20) not null,
-> sex enum(‘male‘,‘female‘) not null default ‘male‘,
-> age int(3) unsigned not null default 28,
-> hire_date date not null
-> ,post_comment varchar(100),
-> salary double(15,2),
-> office int,
-> depart_id int
-> );
Query OK, 0 rows affected (0.04 sec)
# 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_comment | varchar(100) | YES | | NULL | |
| salary | double(15,2) | YES | | NULL | |
| office | int(11) | YES | | NULL | |
| depart_id | int(11) | YES | | NULL | |
+--------------+-----------------------+------+-----+---------+----------------+
9 rows in set (0.01 sec)
#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)
;
#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
select name,salary*12 from employee;
select name,salary*12 as Annual_salary from employee;
select name,salary*12 Annual_salary from employee;
# 定義顯式格式
concat（）函數用於連接字符串
mysql> 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
mysql> select concat_ws(‘:‘,name,salary*12) as Annual_salary from employee;
1、查出所有員工的名字，薪資,格式為 < 名字:egon > < 薪資:3000 > mysql> select concat(‘<名字:‘,name,‘> ‘,‘<薪資:‘,salary,‘>‘) from employee; 2、 查出所有的崗位（去掉重復） mysql> select distinct depart_id from employee; 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 mysql> select name, salary*12 annual_salary from employee;
四 where約束
where字句中可以使用：
- 比較運算符：><>=<=<>!=
- between 80 and 100 值在80到100之間
- in(80,90,100)值是80或90或100
- like ‘egon%’,pattern 可以是%或_, %：表示任意多字符； _:表示一個字符
- 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=‘‘; 註意‘‘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__‘;
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範圍內的員工姓名、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%‘;
五 分組查詢：group by
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
#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 #！！！註意 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中的值要麽是來自於聚集函數的結果，要麽是來自於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‘; ！！！SQL_MODE設置！！！
mysql> select @@global.sql_mode; +-------------------+ | @@global.sql_mode | +-------------------+ | | +-------------------+ 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 | +----+------+--------+-----+------------+----------------------------+--------------+------------+--------+-----------+ 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 #設置成功後，一定要退出，然後重新登錄方可生效 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 | +----------------------------+-----------+ rows in set (0.00 sec)
三 GROUP BY
單獨使用GROUP BY關鍵字分組
SELECT post FROM employee GROUP BY post;
註意：我們按照post字段分組，那麽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
五 小練習：
1. 查詢崗位名以及崗位包含的所有員工名字 mysql> select post,group_concat(name) from employee group by post; +-----------------------------------------+---------------------------------------------------------+ | post | group_concat(name) | +-----------------------------------------+---------------------------------------------------------+ | operation | 程咬鐵,程咬銅,程咬銀,程咬金,張野 | | sale | 格格,星星,丁丁,丫丫,歪歪 | | teacher | 成龍,jinxin,jingliyang,liwenzhou,yuanhao,wupeiqi,alex | | 老男孩駐沙河辦事處外交大使 | egon | +-----------------------------------------+---------------------------------------------------------+ 2. 查詢崗位名以及各崗位內包含的員工個數 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 | +-----------------------------------------+-----------+ 3. 查詢公司內男員工和女員工的個數 mysql> select sex, count(id) from employee group by sex; +--------+-----------+ | sex | count(id) | +--------+-----------+ | male | 10 | | female | 8 | +--------+-----------+ 4. 查詢崗位名以及各崗位的平均薪資 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 | +-----------------------------------------+---------------+ 5. 查詢崗位名以及各崗位的最高薪資 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 | +-----------------------------------------+-------------+ 6. 查詢崗位名以及各崗位的最低薪資 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 | +-----------------------------------------+-------------+ 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 mysql> select sex,avg(salary) from employee group by sex; +--------+---------------+ | sex | avg(salary) | +--------+---------------+ | male | 110920.077000 | | female | 7250.183750 | +--------+---------------+
六 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，但是均對不能使用聚合函數 # 2. having發生在分組group by之後，因而having中可以使用分組的字段，無法直接取到其它字段，可以使用聚合函數 mysql> select @@sql_mode; +--------------------+ | @@sql_mode | +--------------------+ | ONLY_FULL_GROUP_BY | +--------------------+ 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 | +----+------+------+-----+------------+---------+--------------+------------+--------+-----------+ 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，分組後無法直接取到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 | +-----------+-------------------------------------------------------+ rows in set (0.00 sec)
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 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 | +-----------------------------------------+--------------------+-----------+ 2. 查詢各崗位平均薪資大於10000的崗位名、平均工資 mysql> select post,avg(salary) from employee group by post having avg(salary)>10000; +-----------+---------------+ | post | avg(salary) | +-----------+---------------+ | operation | 16800.026000 | | teacher | 151842.901429 | +-----------+---------------+ 3. 查詢各崗位平均薪資大於10000且小於20000的崗位名、平均工資 mysql> select post,avg(salary) from employee group by post having avg(salary) between 10000 and 20000; +-----------+--------------+ | post | avg(salary) | +-----------+--------------+ | operation | 16800.026000 | +-----------+--------------+
七 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 mysql> select * from employee order by age,hire_date desc; 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 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 | +-----------+---------------+ 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 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 | +-----------+---------------+
八 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，然後包含這一條在內往後查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，然後包含這一條在內往後查5條
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 | +----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+ 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 | +----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+ 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 | +----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+ rows in set (0.00 sec)
九 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]$‘;
數據庫：數據操作-單表查詢