Comment MySQL implémente-t-il une requête à table unique ? Cet article vous présentera la méthode de requête de table unique MySQL. Il a une certaine valeur de référence. Les amis dans le besoin peuvent s'y référer. J'espère qu'il vous sera utile.
Nous créons d'abord une table et insérons des données :
# 创建表
mysql> create table company.employee5(
id int primary key AUTO_INCREMENT not null,
name varchar(30) not null,
sex enum('male','female') default 'male' not null,
hire_date date not null,
post varchar(50) not null,
job_description varchar(100),
salary double(15,2) not null,
office int,
dep_id int
);
# 插入数据
mysql> insert into company.employee5(name,sex,hire_date,post,job_description,salary,office,dep_id) values
('jack','male','20180202','instructor','teach',5000,501,100),
('tom','male','20180203','instructor','teach',5500,501,100),
('robin','male','20180202','instructor','teach',8000,501,100),
('alice','female','20180202','instructor','teach',7200,501,100),
('tianyun','male','20180202','hr','hrcc',600,502,101),
('harry','male','20180202','hr',NULL,6000,502,101),
('emma','female','20180206','sale','salecc',20000,503,102),
('christine','female','20180205','sale','salecc',2200,503,102),
('zhuzhu','male','20180205','sale',NULL,2200,503,102),
('gougou','male','20180205','sale','',2200,503,102);
# 查看表结构
mysql> desc employee5;
+-----------------+-----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------------+-----------------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(30) | NO | | NULL | |
| sex | enum('male','female') | NO | | male | |
| hire_date | date | NO | | NULL | |
| post | varchar(50) | NO | | NULL | |
| job_description | varchar(100) | YES | | NULL | |
| salary | double(15,2) | NO | | NULL | |
| office | int(11) | YES | | NULL | |
| dep_id | int(11) | YES | | NULL | |
+-----------------+-----------------------+------+-----+---------+----------------+Copier après la connexion
Syntaxe de requête
SELECT 字段1,字段2... FROM 表名
WHERE 条件
GROUP BY field
HAVING 筛选
ORDER BY field
LIMIT 限制条数；
Copier après la connexion
Affichez toutes les données de la table
mysql> select * from employee5;
+----+-----------+--------+------------+------------+-----------------+----------+--------+--------+
| id | name | sex | hire_date | post | job_description | salary | office | dep_id |
+----+-----------+--------+------------+------------+-----------------+----------+--------+--------+
| 1 | jack | male | 2018-02-02 | instructor | teach | 5000.00 | 501 | 100 |
| 2 | tom | male | 2018-02-03 | instructor | teach | 5500.00 | 501 | 100 |
| 3 | robin | male | 2018-02-02 | instructor | teach | 8000.00 | 501 | 100 |
| 4 | alice | female | 2018-02-02 | instructor | teach | 7200.00 | 501 | 100 |
| 5 | tianyun | male | 2018-02-02 | hr | hrcc | 600.00 | 502 | 101 |
| 6 | harry | male | 2018-02-02 | hr | NULL | 6000.00 | 502 | 101 |
| 7 | emma | female | 2018-02-06 | sale | salecc | 20000.00 | 503 | 102 |
| 8 | christine | female | 2018-02-05 | sale | salecc | 2200.00 | 503 | 102 |
| 9 | zhuzhu | male | 2018-02-05 | sale | NULL | 2200.00 | 503 | 102 |
| 10 | gougou | male | 2018-02-05 | sale | | 2200.00 | 503 | 102 |
+----+-----------+--------+------------+------------+-----------------+----------+--------+--------+
10 rows in set (0.00 sec)
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Requête simple
Requête simple
mysql> SELECT * FROM employee5;
mysql> SELECT name, salary, dep_id FROM employee5;
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Déduplication DISTINCT
mysql> SELECT post FROM employee5;
mysql> SELECT DISTINCT post FROM employee5;
注：不能部分使用DISTINCT，通常仅用于某一字段。
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Requête via quatre opérations arithmétiques
mysql> SELECT name, salary, salary*14 FROM employee5;
mysql> SELECT name, salary, salary*14 AS Annual_salary FROM employee5;
mysql> SELECT name, salary, salary*14 Annual_salary FROM employee5;
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Définir le format d'affichage
CONCAT() 函数用于连接字符串
mysql> SELECT CONCAT(name, ' annual salary: ', salary*14) AS Annual_salary FROM employee5;
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Requête conditionnelle
a、语法
select * from 表名 where 条件
b、比较运算符
大于 小于 大于等于 小于等于 不等于 > < >= <=
!=或<>
c、逻辑运算符
并且 或者 非 and or notd、模糊查询
like % 表示任意多个任意字符
_ 表示一个任意字符
e、范围查询 in 表示在一个非连续的范围内
between...and... 表示在一个连续的范围内
f、空判断
判断空：is null
判断非空：is not null
g、优先级
小括号,not 比较运算符， 逻辑运算符
and比or优先级高，如果同时出现并希望先选or，需要结合()来使用Copier après la connexion
Requête à condition unique
mysql> SELECT name,post FROM employee5 WHERE post='hr';
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Requête à conditions multiples
mysql> SELECT name,salary FROM employee5 WHERE post='hr' AND salary>5000;
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Mot clé ENTRE ET requête
mysql> SELECT name,salary FROM employee5 WHERE salary BETWEEN 5000 AND 15000;
mysql> SELECT name,salary FROM employee5 WHERE salary NOT BETWEEN 5000 AND 15000;
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Requête de mot clé EST NULL
mysql> SELECT name,job_description FROM employee5 WHERE job_description IS NULL;
mysql> SELECT name,job_description FROM employee5 WHERE job_description IS NOT NULL;
mysql> SELECT name,job_description FROM employee5 WHERE job_description='';
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Requête de mot clé IN définie
mysql> SELECT name, salary FROM employee5 WHERE salary=4000 OR salary=5000 OR salary=6000 OR salary=9000 ;
mysql> SELECT name, salary FROM employee5 WHERE salary IN (4000,5000,6000,9000) ;
mysql> SELECT name, salary FROM employee5 WHERE salary NOT IN (4000,5000,6000,9000) ;
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Requête floue de mot clé LIKE
通配符’%’
mysql> SELECT * FROM employee5 WHERE name LIKE 'al%';
通配符’_’
mysql> SELECT * FROM employee5 WHERE name LIKE 'al___';
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Tri des requêtes
Trier par une seule colonne
mysql> SELECT * FROM employee5 ORDER BY salary;
mysql> SELECT name, salary FROM employee5 ORDER BY salary ASC;
mysql> SELECT name, salary FROM employee5 ORDER BY salary DESC;
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Trier par plusieurs colonnes
mysql> SELECT * FROM employee5 ORDER BY hire_date DESC,salary ASC;
# 先按入职时间，再按薪水排序
mysql> SELECT * FROM employee5 ORDER BY hire_date DESC, salary DESC;
# 先按职位，再按薪水排序
mysql> SELECT * FROM employee5 ORDER BY post, salary DESC;
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Limite des requêtes de pagination
mysql> SELECT * FROM employee5 ORDER BY salary DESC LIMIT 5; //默认初始位置为0
mysql> SELECT * FROM employee5 ORDER BY salary DESC LIMIT 0,5;
mysql> SELECT * FROM employee5 ORDER BY salary DESC LIMIT 3,5; //从第4条开始，共显示5条
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Requête de fonction d'agrégation
a、count(*) 表示计算总行数，括号中可以写*和列名
b、max(列) 表示求此列的最大值
c、min(列) 表示求此列的最小值
d、sun(列) 表示求此列的和
e、avg(列) 表示求此列的平均值
mysql> SELECT COUNT(*) FROM employee5;
mysql> SELECT COUNT(*) FROM employee5 WHERE dep_id=101;
mysql> SELECT MAX(salary) FROM employee5;
mysql> SELECT MIN(salary) FROM employee5;
mysql> SELECT AVG(salary) FROM employee5;
mysql> SELECT SUM(salary) FROM employee5;
mysql> SELECT SUM(salary) FROM employee5 WHERE dep_id=101;
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Requête de groupe
# 单独使用GROUP BY关键字分组
mysql> SELECT post FROM employee5 GROUP BY post;
注意：我们按照post字段分组，那么select查询的字段只能是post，想要获取组内的其他相关信息，需要借助函数
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Le mot-clé GROUP BY est utilisé avec la fonction group_concat()
# 按照id分组，并查看组内成员
mysql> SELECT dep_id,GROUP_CONCAT(name) FROM employee5 GROUP BY dep_id;
mysql> SELECT dep_id,GROUP_CONCAT(name) as emp_members FROM employee5 GROUP BY dep_id;
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GROUP BY est utilisé avec la set function
# 按照dep_id 分组， 并计算组内成员工资总和
mysql> SELECT dep_id,SUM(salary) FROM employee5 GROUP BY dep_id;
# 按照dep_id分组，并计算组内成员工资平均值
mysql> SELECT dep_id,AVG(salary) FROM employee5 GROUP BY dep_id;
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Requête d'expression régulière
mysql> SELECT * FROM employee5 WHERE name REGEXP '^j';
mysql> SELECT * FROM employee5 WHERE salary REGEXP '[5]+.*';
mysql> SELECT * FROM employee5 WHERE salary REGEXP '[5]{2}.*';Copier après la connexion
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