文章目录

一、查询记录

SELECT select_expr [, select expr ..]
[
FROM table_ references
[WHERE条件]
[GROUP BY {col_name | position} [ASC | DESC], ...分组]
[HAVING条件对分组结果进行二次筛选]
[ORDER BY {col_name | position} [ASC | DESC], ..排序]
[LIMIT限制显示条数]
]

二、查询表达式

每一个表达式表示想要的一列，必须至少有一列，多个列之间以逗号隔开
'*'表示所有列,tbI_name. *可以表示命名表的所有列
查询长达式可以使用[AS]alias_name为其赋予别名

1.测试查询

以下两种查询方式效果相同

（1）查询

SELECT * FROM cms_admin; 
SELECT cms_admin.* FROM cms_admin;

查询表中特定内容
查询管理员编号和名称

SELECT id,username FROM cms_admin;
SELECT username,id,role FROM cms_admin;

表来自于哪个数据库下db_name.tbl_name

SELECT id,username,role FROM cms.cms_admin;

字段来自于哪张表

SELECT cms_admin.id,cms_admin.username FROM cms.cms_admin;

（2）为表、字段️起别名

给表名起别名

SELECT id,username FROM cms_admin AS a;
SELECT id,username FROM cms_admin a;
SELECT a.id,a.username,a.email,a.role FROM cms_admin AS a;

给字段起别名

SELECT id AS '编号',username AS '用户名',email AS '邮箱',role '角色' FROM cms_admin;

结果：
mysql> SELECT id AS '编号',username AS '用户名',email AS '邮箱',role ' 角色' FROM cms_admin;
+------+--------+--------------+------------+
| 编号     | 用户名      | 邮箱             | 角色          |
+------+--------+--------------+------------+
|    1 | admin  | [email protected] | 超级管理员          |
|    2 | king   | [email protected] | 普通管理员         |
|    3 | 麦子       | [email protected] | 普通管理员         |
|    4 | queen  | [email protected] | 普通管理员         |
|    5 | test   | [email protected] | 普通管理员         |
+------+--------+--------------+------------+

SELECT a.id AS i,a.username AS u,a.email as e,a.role AS r FROM cms_admin AS a; 

结果：
mysql> SELECT a.id AS i,a.username AS u,a.email as e,a.role AS r FROM cms_admin AS a;
+---+-------+--------------+------------+
| i | u     | e            | r          |
+---+-------+--------------+------------+
| 1 | admin | [email protected] | 超级管理员          |
| 2 | king  | [email protected] | 普通管理员         |
| 3 | 麦子      | [email protected] | 普通管理员         |
| 4 | queen | [email protected] | 普通管理员         |
| 5 | test  | [email protected] | 普通管理员         |
+---+-------+--------------+------------+

SELECT id AS proId,proId AS id,username FROM cms_user;

SELECT 1,2,3,4,5,id,username FROM cms_user;

三、WHERE 条件

1.简介

2.带WHERE条件的查询

（1）WHERE条件

查询编号为1的用户

SELECT id,username,email FROM cms_user WHERE id=1;
SELECT id,username,email FROM cms_user WHERE username='king';

查询编号不为1的用户

SELECT  * FROM cms_user WHERE id!=1;
SELECT  * FROM cms_user WHERE id<>1;

添加age字段

ALTER TABLE cms_user ADD age TINYINT UNSIGNED DEFAULT 18;
INSERT cms_user(username,password,regTime,proId,age)
VALUES('test1','test1',1419811708,1,NULL);

查询表中记录age值为NULL

SELECT * FROM cms_user WHERE age=NULL;
结果：
mysql> SELECT * FROM cms_user WHERE age=NULL;
Empty set (0.00 sec)

#检测null需要用<=>
SELECT * FROM cms_user WHERE age<=>NULL;
结果：
mysql> SELECT * FROM cms_user WHERE age<=>NULL;
+----+----------+----------+-------------+------------+----------+-------+------+
| id | username | password | email       | regTime    | face     | proId | age  |
+----+----------+----------+-------------+------------+----------+-------+------+
| 12 | test1    | test1    | [email protected] | 1419811708 | user.jpg |     1 | NULL |
+----+----------+----------+-------------+------------+----------+-------+------+
1 row in set (0.00 sec)

SELECT * FROM cms_user WHERE age<=>18;

IS NULL 或者IS NOT NULL

SELECT * FROM cms_user WHERE age IS NULL;

（2）BETWEEN、IN 的用法

查询编号在3~10之间的用户

SELECT * FROM cms_user WHERE id BETWEEN 3 AND 10;

查询编号为1，3，5，7，9，11，13，100

SELECT * FROM cms_user WHERE id IN(1,3,5,7,9,11,13,100,1000);

– 查询proId为1 和3的用户

SELECT * FROM cms_user WHERE proId IN(1,3);

查询用户名为king,queen,张三，章子怡的记录

SELECT * FROM cms_user WHERE username IN('king','queen','张三','章子怡');

3.模糊查询

（1）简介

%:代表0个一个或者多个任意字符
_:代表1个任意字符

（2）测试模糊查询

查询姓张的用户

SELECT * FROM cms_user WHERE username LIKE '张%';

查询用户名中包含in的用户

SELECT * FROM cms_user WHERE username LIKE '%in%';
SELECT * FROM cms_user WHERE username LIKE '%';

查询用户名为3位的用户

SELECT * FROM cms_user WHERE username LIKE '___';

-用户名_i%

SELECT * FROM cms_user WHERE username LIKE '_I%';
SELECT * FROM cms_user WHERE username LIKE 'king';
SELECT * FROM cms_user WHERE username NOT LIKE '_I%';

查询用户名为king并且密码为king的用户

SELECT * FROM cms_user WHERE username='king' AND password='king';

查询编号大于等于3的变量年龄不为NULL的用户

SELECT * FROM cms_user WHERE id>=3 AND age IS NOT NULL;

查询编号大于等于3的变量年龄不为NULL的用户并且proId为的3

SELECT * FROM cms_user WHERE id>=3 AND age IS NOT NULL AND proId=3;

查询编号在5~10的用户并且用户名为4位的用户

SELECT * FROM cms_user WHERE id BETWEEN 5 AND 10 AND username LIKE '____';

查询用户名以张开始或者用户所在身份为2,4的记录

SELECT * FROM cms_user WHERE username LIKE '张%' OR proId IN(2,4);SELECT

四、分组查询

配合GROUP_ CONCAT()得到分组详情
配合聚函数
COUNT()
MAX()
MIN()
AVG()
SUM()
配合WITH ROLLUP记录上面所有记录的总和

测试：

按照用户所属身份分组proId

SELECT * FROM cms_user GROUP BY proId;

向用户表中添加性别字段

ALTER TABLE cms_user ADD sex ENUM('男','女','保密');
UPDATE cms_user SET sex='男' WHERE id IN(1,3,5,7,9);
UPDATE cms_user SET sex='女' WHERE id IN(2,4,6,8,10);
UPDATE cms_user SET sex='保密' WHERE id IN(12,11);

按照用户性别分组

SELECT * FROM cms_user GROUP BY sex;

按照字段位置分组

SELECT * FROM cms_user GROUP BY 7;

按照多个字段分组

SELECT * FROM cms_user GROUP BY sex,proId;

查询编号大于等于5的用户按照sex分组

SELECT * FROM cms_user WHERE id>=5 GROUP BY sex;

1.GROUP_ CONCAT()得到分组详情

查询id,sex,用户名详情按照性别分组

SELECT id,sex,GROUP_CONCAT(username) FROM cms_user GROUP BY sex;
结果：
mysql> SELECT id,sex,GROUP_CONCAT(username) FROM cms_user GROUP BY sex;
+----+------+-----------------------------+
| id | sex  | GROUP_CONCAT(username)      |
+----+------+-----------------------------+
|  1 | 男     | 张三,rose,king,ring,章子怡            |
|  4 | 女    | long,queen,blek,张三丰,lily       |
| 11 | 保密     | john,test1                  |
+----+------+-----------------------------+

2.分组查询配合聚合函数

-查询proId，性别详情，注册时间详情，用户名详情按照proId

SELECT proId,GROUP_CONCAT(username),GROUP_CONCAT(sex),GROUP_CONCAT(regTime) FROM cms_user GROUP BY proId;

更新年龄

UPDATE cms_user SET age=11 WHERE id=1;
UPDATE cms_user SET age=21 WHERE id=2;
UPDATE cms_user SET age=33 WHERE id=3;
UPDATE cms_user SET age=44 WHERE id=4;
UPDATE cms_user SET age=25 WHERE id=5;
UPDATE cms_user SET age=77 WHERE id=6;
UPDATE cms_user SET age=56 WHERE id=7;
UPDATE cms_user SET age=88 WHERE id=8;
UPDATE cms_user SET age=12 WHERE id=9;
UPDATE cms_user SET age=32 WHERE id=10;
UPDATE cms_user SET age=65 WHERE id=11;

查询编号,sex,用户名详情以及组中总人数按照sex分组

SELECT id,sex,GROUP_CONCAT(username) AS users,COUNT(*) AS totalUsers FROM cms_user GROUP BY sex;

统计表中所有记录

SELECT COUNT(*) AS totalUsers FROM cms_user;
SELECT COUNT(id) AS totalUsers FROM cms_user;
#以上两个表达效果一样
mysql> SELECT COUNT(id) AS totalUsers FROM cms_user;
+------------+
| totalUsers |
+------------+
|         12 |
+------------+

COUNT(字段)不统计NULL值

SELECT COUNT(age) AS totalUsers FROM cms_user;

聚合函数
查询编号,性别,用户名详情，组中总人数，组中最大年龄，最小年龄，平均年龄，以及年龄总和按照性别分组

SELECT id,sex,GROUP_CONCAT(username),
COUNT(*) AS totalUsers,
MAX(age) AS max_age,
MIN(age) AS min_age,
AVG(age) AS avg_age,
SUM(age) AS sum_age
FROM cms_user
GROUP BY sex;

WITH ROLLUP 在group分组字段的基础上再进行统计数据

SELECT id,sex,
COUNT(*) AS totalUsers,
MAX(age) AS max_age,
MIN(age) AS min_age
FROM cms_user
GROUP BY sex WITH ROLLUP;

结果：
+----+------+------------+---------+---------+
| id | sex  | totalUsers | max_age | min_age |
+----+------+------------+---------+---------+
|  1 | 男     |          5 |      18 |      18 |
|  4 | 女    |          5 |      18 |      18 |
| 11 | 保密     |          2 |      18 |      18 |
| 11 | NULL |         12 |      18 |      18 |
+----+------+------------+---------+---------+

五、having语句对分组结果进行二次筛选

二次筛选
查询性别sex,用户名详情,组中总人数，最大年龄，年龄总和,根据性别分组

SELECT sex,GROUP_CONCAT(username) AS users,
COUNT(*) AS totalUsers,
MAX(age) AS max_age,
SUM(age) AS sum_age
FROM cms_user 
GROUP BY sex;

查询组中人数大于2的

SELECT sex,GROUP_CONCAT(username) AS users,
COUNT(*) AS totalUsers,
MAX(age) AS max_age,
SUM(age) AS sum_age
FROM cms_user 
GROUP BY sex
HAVING COUNT(*)>2;

查询组中人数大于2并且最大年龄大于60的

SELECT sex,GROUP_CONCAT(username) AS users,
COUNT(*) AS totalUsers,
MAX(age) AS max_age,
SUM(age) AS sum_age
FROM cms_user 
GROUP BY sex
HAVING COUNT(*)>2 AND MAX(age)>60;

查询编号大于等于2的用户

SELECT sex,GROUP_CONCAT(username) AS users,
COUNT(*) AS totalUsers,
MAX(age) AS max_age,
SUM(age) AS sum_age
FROM cms_user 
WHERE id>=2
GROUP BY sex
HAVING COUNT(*)>2 AND MAX(age)>60;

SELECT id,sex,GROUP_CONCAT(username) AS users,
COUNT(*) AS totalUsers,
MAX(age) AS max_age,
SUM(age) AS sum_age
FROM cms_user 
WHERE id>=2
HAVING COUNT(*)>2 AND MAX(age)>60;

数据库Ⅴ——查询数据操作（1）

文章目录

一、查询记录

二、查询表达式

1.测试查询

（1）查询

（2）为表、字段️起别名

三、WHERE 条件

1.简介

2.带WHERE条件的查询

（1）WHERE条件

（2）BETWEEN、IN 的用法

3.模糊查询

（1）简介

（2）测试模糊查询

四、分组查询

1.GROUP_ CONCAT()得到分组详情

2.分组查询配合聚合函数

五、having语句对分组结果进行二次筛选

DAPPER 事务 TRANSACTION

數據庫Ⅳ——數據的操作

Linux基礎命令Ⅲ——目錄的創建刪除

數據庫Ⅲ（2）——修改表結構

數據庫Ⅲ（1）——完整性約束條件測試

數據結構與算法——總結篇（算法效率、排序方法）

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