文章目錄

一、查詢記錄

SELECT select_expr [, select expr ..]
[
FROM table_ references
[WHERE條件]
[GROUP BY {col_name | position} [ASC | DESC], ...分組]
[HAVING條件對分組結果進行二次篩選]
[ORDER BY {col_name | position} [ASC | DESC], ..排序]
[LIMIT限制顯示條數]
]

二、查詢表達式

每一個表達式表示想要的一列，必須至少有一列，多個列之間以逗號隔開
'*'表示所有列,tbI_name. *可以表示命名錶的所有列
查詢長達式可以使用[AS]alias_name爲其賦予別名

1.測試查詢

以下兩種查詢方式效果相同

（1）查詢

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

查詢表中特定內容
查詢管理員編號和名稱

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

表來自於哪個數據庫下db_name.tbl_name

SELECT id,username,role FROM cms.cms_admin;

字段來自於哪張表

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

（2）爲表、字段️起別名

給表名起別名

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;

給字段起別名

SELECT id AS '編號',username AS '用戶名',email AS '郵箱',role '角色' FROM cms_admin;

結果：
mysql> SELECT id AS '編號',username AS '用戶名',email AS '郵箱',role ' 角色' FROM cms_admin;
+------+--------+--------------+------------+
| 編號     | 用戶名      | 郵箱             | 角色          |
+------+--------+--------------+------------+
|    1 | admin  | [email protected] | 超級管理員          |
|    2 | king   | [email protected] | 普通管理員         |
|    3 | 麥子       | [email protected] | 普通管理員         |
|    4 | queen  | [email protected] | 普通管理員         |
|    5 | test   | [email protected] | 普通管理員         |
+------+--------+--------------+------------+

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

結果：
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] | 超級管理員          |
| 2 | king  | [email protected] | 普通管理員         |
| 3 | 麥子      | [email protected] | 普通管理員         |
| 4 | queen | [email protected] | 普通管理員         |
| 5 | test  | [email protected] | 普通管理員         |
+---+-------+--------------+------------+

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

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

三、WHERE 條件

1.簡介

2.帶WHERE條件的查詢

（1）WHERE條件

查詢編號爲1的用戶

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

查詢編號不爲1的用戶

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);

查詢表中記錄age值爲NULL

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

#檢測null需要用<=>
SELECT * FROM cms_user WHERE age<=>NULL;
結果：
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

查詢編號在3~10之間的用戶

SELECT * FROM cms_user WHERE id BETWEEN 3 AND 10;

查詢編號爲1，3，5，7，9，11，13，100

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

– 查詢proId爲1 和3的用戶

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

查詢用戶名爲king,queen,張三，章子怡的記錄

SELECT * FROM cms_user WHERE username IN('king','queen','張三','章子怡');

3.模糊查詢

（1）簡介

%:代表0個一個或者多個任意字符
_:代表1個任意字符

（2）測試模糊查詢

查詢姓張的用戶

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

查詢用戶名中包含in的用戶

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

查詢用戶名爲3位的用戶

SELECT * FROM cms_user WHERE username LIKE '___';

-用戶名_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%';

查詢用戶名爲king並且密碼爲king的用戶

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

查詢編號大於等於3的變量年齡不爲NULL的用戶

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

查詢編號大於等於3的變量年齡不爲NULL的用戶並且proId爲的3

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

查詢編號在5~10的用戶並且用戶名爲4位的用戶

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

查詢用戶名以張開始或者用戶所在身份爲2,4的記錄

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

四、分組查詢

配合GROUP_ CONCAT()得到分組詳情
配合聚函數
COUNT()
MAX()
MIN()
AVG()
SUM()
配合WITH ROLLUP記錄上面所有記錄的總和

測試：

按照用戶所屬身份分組proId

SELECT * FROM cms_user GROUP BY proId;

向用戶表中添加性別字段

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);

按照用戶性別分組

SELECT * FROM cms_user GROUP BY sex;

按照字段位置分組

SELECT * FROM cms_user GROUP BY 7;

按照多個字段分組

SELECT * FROM cms_user GROUP BY sex,proId;

查詢編號大於等於5的用戶按照sex分組

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

1.GROUP_ CONCAT()得到分組詳情

查詢id,sex,用戶名詳情按照性別分組

SELECT id,sex,GROUP_CONCAT(username) FROM cms_user GROUP BY sex;
結果：
mysql> SELECT id,sex,GROUP_CONCAT(username) FROM cms_user GROUP BY sex;
+----+------+-----------------------------+
| id | sex  | GROUP_CONCAT(username)      |
+----+------+-----------------------------+
|  1 | 男     | 張三,rose,king,ring,章子怡            |
|  4 | 女    | long,queen,blek,張三丰,lily       |
| 11 | 保密     | john,test1                  |
+----+------+-----------------------------+

2.分組查詢配合聚合函數

-查詢proId，性別詳情，註冊時間詳情，用戶名詳情按照proId

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

更新年齡

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;

查詢編號,sex,用戶名詳情以及組中總人數按照sex分組

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

統計表中所有記錄

SELECT COUNT(*) AS totalUsers FROM cms_user;
SELECT COUNT(id) AS totalUsers FROM cms_user;
#以上兩個表達效果一樣
mysql> SELECT COUNT(id) AS totalUsers FROM cms_user;
+------------+
| totalUsers |
+------------+
|         12 |
+------------+

COUNT(字段)不統計NULL值

SELECT COUNT(age) AS totalUsers FROM cms_user;

聚合函數
查詢編號,性別,用戶名詳情，組中總人數，組中最大年齡，最小年齡，平均年齡，以及年齡總和按照性別分組

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分組字段的基礎上再進行統計數據

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

結果：
+----+------+------------+---------+---------+
| 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語句對分組結果進行二次篩選

二次篩選
查詢性別sex,用戶名詳情,組中總人數，最大年齡，年齡總和,根據性別分組

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;

查詢組中人數大於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;

查詢組中人數大於2並且最大年齡大於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;

查詢編號大於等於2的用戶

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;

數據庫Ⅴ——查詢數據操作（1）

文章目錄

一、查詢記錄

二、查詢表達式

1.測試查詢

（1）查詢

（2）爲表、字段️起別名

三、WHERE 條件

1.簡介

2.帶WHERE條件的查詢

（1）WHERE條件

（2）BETWEEN、IN 的用法

3.模糊查詢

（1）簡介

（2）測試模糊查詢

四、分組查詢

1.GROUP_ CONCAT()得到分組詳情

2.分組查詢配合聚合函數

五、having語句對分組結果進行二次篩選

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