表的增删改查（MySQL）

INSERT [INTO] table_name 
 [(column [, column] ...)] 
 VALUES (value_list) [, (value_list)] ...
 
value_list: value, [, value] ...

-- 创建一张学生表
CREATE TABLE students (
   id INT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
   sn INT NOT NULL UNIQUE COMMENT '学号',
   name VARCHAR(20) NOT NULL,
   qq VARCHAR(20)
);

-- 插入两条记录，value_list 数量必须和定义表的列的数量及顺序一致
-- 注意，这里在插入的时候，也可以不用指定id(当然，那时候就需要明确插入数据到那些列了)，那么mysql会使用默认的值进行自增。

INSERT INTO students VALUES (100, 10000, '唐三藏', NULL);
Query OK, 1 row affected (0.02 sec)

INSERT INTO students VALUES (101, 10001, '孙悟空', '11111');
Query OK, 1 row affected (0.02 sec)

-- 查看插入结果
SELECT * FROM students;
+-----+-------+-----------+-------+
| id | sn   | name     | qq   |
+-----+-------+-----------+-------+
| 100 | 10000 | 唐三藏     | NULL |
| 101 | 10001 | 孙悟空     | 11111 |
+-----+-------+-----------+-------+
2 rows in set (0.00 sec)

-- 插入两条记录，value_list 数量必须和指定列数量及顺序一致
INSERT INTO students (id, sn, name) VALUES 
 (102, 20001, '曹孟德'), 
 (103, 20002, '孙仲谋');
Query OK, 2 rows affected (0.02 sec)
Records: 2 Duplicates: 0  Warnings: 0

-- 查看插入结果
SELECT * FROM students;
+-----+-------+-----------+-------+
| id | sn   | name     | qq   |
+-----+-------+-----------+-------+
| 100 | 10000 | 唐三藏     | NULL |
| 101 | 10001 | 孙悟空     | 11111 |
| 102 | 20001 | 曹孟德     | NULL |
| 103 | 20002 | 孙仲谋     | NULL |
+-----+-------+-----------+-------+
4 rows in set (0.00 sec)

-- 主键冲突
INSERT INTO students (id, sn, name) VALUES (100, 10010, '唐大师');
ERROR 1062 (23000): Duplicate entry '100' for key 'PRIMARY'

-- 唯一键冲突
INSERT INTO students (sn, name) VALUES (20001, '曹阿瞒');
ERROR 1062 (23000): Duplicate entry '20001' for key 'sn'

INSERT ... ON DUPLICATE KEY UPDATE 
 column = value [, column = value] ... 

INSERT INTO students (id, sn, name) VALUES (100, 10010, '唐大师')
 ON DUPLICATE KEY UPDATE sn = 10010, name = '唐大师';
Query OK, 2 rows affected (0.47 sec)
-- 0 row affected: 表中有冲突数据，但冲突数据的值和 update 的值相等
-- 1 row affected: 表中没有冲突数据，数据被插入
-- 2 row affected: 表中有冲突数据，并且数据已经被更新
-- 通过 MySQL 函数获取受到影响的数据行数
SELECT ROW_COUNT();
+-------------+
| ROW_COUNT() |
+-------------+
|           2 |
+-------------+
1 row in set (0.00 sec)

-- ON DUPLICATE KEY 当发生重复key的时候

-- 主键 或者 唯一键 没有冲突，则直接插入；
-- 主键 或者 唯一键 如果冲突，则删除后再插入

REPLACE INTO students (sn, name) VALUES (20001, '曹阿瞒');
Query OK, 2 rows affected (0.00 sec)

-- 1 row affected: 表中没有冲突数据，数据被插入
-- 2 row affected: 表中有冲突数据，删除后重新插入

SELECT 
 [DISTINCT] {* | {column [, column] ...} 
 [FROM table_name] 
 [WHERE ...] 
 [ORDER BY column [ASC | DESC], ...] 
 LIMIT ... 

-- 创建表结构 
CREATE TABLE exam_result ( 
 id INT UNSIGNED PRIMARY KEY AUTO_INCREMENT, 
 name VARCHAR(20) NOT NULL COMMENT '同学姓名', 
 chinese float DEFAULT 0.0 COMMENT '语文成绩', 
 math float DEFAULT 0.0 COMMENT '数学成绩', 
 english float DEFAULT 0.0 COMMENT '英语成绩' 
); 
 
-- 插入测试数据 
INSERT INTO exam_result (name, chinese, math, english) VALUES 
 ('唐三藏', 67, 98, 56), 
 ('孙悟空', 87, 78, 77), 
 ('猪悟能', 88, 98, 90), 
 ('曹孟德', 82, 84, 67), 
 ('刘玄德', 55, 85, 45), 
 ('孙权', 70, 73, 78), 
 ('宋公明', 75, 65, 30); 
Query OK, 7 rows affected (0.00 sec) 
Records: 7 Duplicates: 0 Warnings: 0 

-- 通常情况下不建议使用 * 进行全列查询 
-- 1. 查询的列越多，意味着需要传输的数据量越大； 
-- 2. 可能会影响到索引的使用。（索引待后面课程讲解）

SELECT * FROM exam_result; 

+----+-----------+-------+--------+--------+ 
| id | name      | chinese | math | english |
+----+-----------+-------+--------+--------+ 
|  1 | 唐三藏     |    67 |     98 |     56 |
|  2 | 孙悟空     |    87 |     78 |     77 |
|  3 | 猪悟能     |    88 |     98 |     90 |
|  4 | 曹孟德     |    82 |     84 |     67 |
|  5 | 刘玄德     |    55 |     85 |     45 |
|  6 | 孙权       |    70 |     73 |     78 |
|  7 | 宋公明     |    75 |     65 |     30 |
+----+-----------+-------+--------+--------+
7 rows in set (0.00 sec) 

-- 指定列的顺序不需要按定义表的顺序来 
SELECT id, name, english FROM exam_result;
+----+-----------+--------+ 
+----+-----------+--------+ 
| id | name      | english | 
+----+-----------+--------+ 
|  1 | 唐三藏     |     56 | 
|  2 | 孙悟空     |     77 | 
|  3 | 猪悟能     |     90 | 
|  4 | 曹孟德     |     67 | 
|  5 | 刘玄德     |     45 | 
|  6 | 孙权       |     78 | 
|  7 | 宋公明     |     30 | 
+----+-----------+--------+ 
7 rows in set (0.00 sec) 

-- 表达式不包含字段 
SELECT id, name, 10 FROM exam_result; 
+----+-----------+----+ 
| id | name      | 10 | 
+----+-----------+----+ 
|  1 | 唐三藏     | 10 | 
|  2 | 孙悟空     | 10 | 
|  3 | 猪悟能     | 10 | 
|  4 | 曹孟德     | 10 | 
|  5 | 刘玄德     | 10 | 
|  6 | 孙权       | 10 | 
|  7 | 宋公明     | 10 | 
+----+-----------+----+ 
7 rows in set (0.00 sec)

-- 表达式包含一个字段 
SELECT id, name, english + 10 FROM exam_result;
+----+-----------+-------------+ 
| id | name      | english + 10 | 
+----+-----------+-------------+ 
|  1 | 唐三藏     |          66 | 
|  2 | 孙悟空     |          87 |
|  3 | 猪悟能     |         100 | 
|  4 | 曹孟德     |          77 | 
|  5 | 刘玄德     |          55 | 
|  6 | 孙权       |          88 | 
|  7 | 宋公明     |          40 | 
+----+-----------+-------------+ 
7 rows in set (0.00 sec) 

-- 表达式包含多个字段 
SELECT id, name, chinese + math + english FROM exam_result; 
+----+-----------+-------------------------+ 
| id | name      | chinese + math + english | 
+----+-----------+-------------------------+ 
|  1 | 唐三藏     |                     221 | 
|  2 | 孙悟空     |                     242 | 
|  3 | 猪悟能     |                     276 | 
|  4 | 曹孟德     |                     233 | 
|  5 | 刘玄德     |                     185 | 
|  6 | 孙权       |                     221 | 
|  7 | 宋公明     |                     170 | 
+----+-----------+-------------------------+ 
7 rows in set (0.00 sec) 

SELECT column [AS] alias_name [...] FROM table_name; 

SELECT id, name, chinese + math + english 总分 FROM exam_result;
+----+-----------+--------+ 
| id | name      | 总分   | 
+----+-----------+--------+ 
|  1 | 唐三藏     |    221 | 
|  2 | 孙悟空     |    242 | 
|  3 | 猪悟能     |    276 | 
|  4 | 曹孟德     |    233 | 
|  5 | 刘玄德     |    185 | 
|  6 | 孙权       |    221 | 
|  7 | 宋公明     |    170 | 
+----+-----------+--------+ 
7 rows in set (0.00 sec) 

-- 98 分重复了
SELECT math FROM exam_result; 
+--------+ 
| math | 
+--------+ 
|     98 | 
|     78 | 
|     98 | 
|     84 | 
|     85 | 
|     73 | 
|     65 | 
+--------+ 
7 rows in set (0.00 sec) 

-- 去重结果
SELECT DISTINCT math FROM exam_result;
+--------+ 
| math | 
+--------+ 
|     98 | 
|     78 | 
|     84 | 
|     85 | 
|     73 | 
|     65 | 
+--------+ 
6 rows in set (0.00 sec) 

-- 基本比较 

SELECT name, english FROM exam_result WHERE english < 60; 
+-----------+--------+ 
| name | english | 
+-----------+--------+ 
| 唐三藏 | 56 | 
| 刘玄德 | 45 | 
| 宋公明 | 30 | 
+-----------+--------+ 
3 rows in set (0.01 sec) 

-- 使用 AND 进行条件连接 
 
SELECT name, chinese FROM exam_result WHERE chinese >= 80 AND chinese <= 90; 
+-----------+-------+ 
| name | chinese | 
+-----------+-------+ 
| 孙悟空 | 87 | 
| 猪悟能 | 88 | 
| 曹孟德 | 82 | 
+-----------+-------+ 
3 rows in set (0.00 sec) 

-- 使用 BETWEEN ... AND ... 条件 
 
SELECT name, chinese FROM exam_result WHERE chinese BETWEEN 80 AND 90; 
+-----------+-------+ 
| name | chinese | 
+-----------+-------+ 
| 孙悟空 | 87 | 
| 猪悟能 | 88 | 
| 曹孟德 | 82 | 
+-----------+-------+ 
3 rows in set (0.00 sec) 

-- 使用 OR 进行条件连接 
 
SELECT name, math FROM exam_result 
 WHERE math = 58 
 OR math = 59 
 OR math = 98 
 OR math = 99; 
+-----------+--------+ 
| name | math | 
+-----------+--------+ 
| 唐三藏 | 98 | 
| 猪悟能 | 98 | 
+-----------+--------+ 
2 rows in set (0.01 sec)

-- 使用 IN 条件 
 
SELECT name, math FROM exam_result WHERE math IN (58, 59, 98, 99); 
+-----------+--------+ 
| name | math | 
+-----------+--------+ 
| 唐三藏 | 98 | 
| 猪悟能 | 98 | 
+-----------+--------+ 
2 rows in set (0.00 sec) 

-- % 匹配任意多个（包括 0 个）任意字符 
 
SELECT name FROM exam_result WHERE name LIKE '孙%'; 
+-----------+ 
| name | 
+-----------+ 
| 孙悟空 | 
| 孙权 | 
+-----------+ 
2 rows in set (0.00 sec) 

-- _ 匹配严格的一个任意字符 
 
SELECT name FROM exam_result WHERE name LIKE '孙_'; 
+--------+ 
| name | 
+--------+ 
| 孙权 | 
+--------+ 
1 row in set (0.00 sec) 

-- WHERE 条件中比较运算符两侧都是字段 
 
SELECT name, chinese, english FROM exam_result WHERE chinese > english; 
+-----------+-------+--------+ 
| name | chinese | english | 
+-----------+-------+--------+ 
| 唐三藏 | 67 | 56 | 
| 孙悟空 | 87 | 77 | 
| 曹孟德 | 82 | 67 | 
| 刘玄德 | 55 | 45 | 
| 宋公明 | 75 | 30 | 
+-----------+-------+--------+ 
5 rows in set (0.00 sec) 

-- WHERE 条件中使用表达式 
-- 别名不能用在 WHERE 条件中 
 
SELECT name, chinese + math + english 总分 FROM exam_result 
 WHERE chinese + math + english < 200; 
+-----------+--------+ 
| name | 总分 | 
+-----------+--------+ 
| 刘玄德 | 185 | 
| 宋公明 | 170 | 
+-----------+--------+ 
2 rows in set (0.00 sec) 

-- AND 与 NOT 的使用 
 
SELECT name, chinese FROM exam_result 
 WHERE chinese > 80 AND name NOT LIKE '孙%'; 
+----+-----------+-------+--------+--------+ 
| id | name | chinese | math | english | 
+----+-----------+-------+--------+--------+ 
| 3 | 猪悟能 | 88 | 98 | 90 | 
| 4 | 曹孟德 | 82 | 84 | 67 | 
+----+-----------+-------+--------+--------+ 
2 rows in set (0.00 sec) 

-- 综合性查询 
 
SELECT name, chinese, math, english, chinese + math + english 总分 
FROM exam_result 
WHERE name LIKE '孙_' OR ( 
 chinese + math + english > 200 AND chinese < math AND english > 80 
); 
+-----------+-------+--------+--------+--------+ 
| name | chinese | math | english | 总分 | 
+-----------+-------+--------+--------+--------+ 
| 猪悟能 | 88 | 98 | 90 | 276 | 
| 孙权 | 70 | 73 | 78 | 221 | 
+-----------+-------+--------+--------+--------+ 
2 rows in set (0.00 sec) 

-- 查询 students 表 
+-----+-------+-----------+-------+ 
| id | sn | name | qq | 
+-----+-------+-----------+-------+ 
| 100 | 10010 | 唐大师 | NULL | 
| 101 | 10001 | 孙悟空 | 11111 | 
| 103 | 20002 | 孙仲谋 | NULL | 
| 104 | 20001 | 曹阿瞒 | NULL | 
+-----+-------+-----------+-------+ 
4 rows in set (0.00 sec) 
 
-- 查询 qq 号已知的同学姓名 
 
SELECT name, qq FROM students WHERE qq IS NOT NULL; 
+-----------+-------+ 
| name | qq | 
+-----------+-------+ 
| 孙悟空 | 11111 | 
+-----------+-------+ 
1 row in set (0.00 sec) 
 
-- NULL 和 NULL 的比较，= 和 <=> 的区别 
 
SELECT NULL = NULL, NULL = 1, NULL = 0; 
+-------------+----------+----------+ 
| NULL = NULL | NULL = 1 | NULL = 0 | 
+-------------+----------+----------+ 
| NULL | NULL | NULL | 
+-------------+----------+----------+ 
1 row in set (0.00 sec) 
 
SELECT NULL <=> NULL, NULL <=> 1, NULL <=> 0; 
+---------------+------------+------------+ 
| NULL <=> NULL | NULL <=> 1 | NULL <=> 0 | 
+---------------+------------+------------+ 
| 1 | 0 | 0 | 
+---------------+------------+------------+ 
1 row in set (0.00 sec) 

-- ASC 为升序（从小到大） 
-- DESC 为降序（从大到小） 
-- 默认为 ASC 
 
SELECT ... FROM table_name [WHERE ...] 
 ORDER BY column [ASC|DESC], [...]; 

SELECT name, math FROM exam_result ORDER BY math; 
+-----------+--------+ 
| name | math | 
+-----------+--------+ 
| 宋公明 | 65 | 
| 孙权 | 73 | 
| 孙悟空 | 78 | 
| 曹孟德 | 84 | 
| 刘玄德 | 85 | 
| 唐三藏 | 98 | 
| 猪悟能 | 98 | 
+-----------+--------+ 
7 rows in set (0.00 sec) 

-- NULL 视为比任何值都小，升序出现在最上面 
 
SELECT name, qq FROM students ORDER BY qq; 
+-----------+-------+ 
| name | qq | 
+-----------+-------+ 
| 唐大师 | NULL | 
| 孙仲谋 | NULL | 
| 曹阿瞒 | NULL | 
| 孙悟空 | 11111 | 
+-----------+-------+ 
4 rows in set (0.00 sec) 

-- NULL 视为比任何值都小，降序出现在最下面 
 
SELECT name, qq FROM students ORDER BY qq DESC; 
+-----------+-------+ 
| name | qq | 
+-----------+-------+ 
| 孙悟空 | 11111 | 
| 唐大师 | NULL | 
| 孙仲谋 | NULL | 
| 曹阿瞒 | NULL | 
+-----------+-------+ 
4 rows in set (0.00 sec)

-- 多字段排序，排序优先级随书写顺序 
 
SELECT name, math, english, chinese FROM exam_result 
 ORDER BY math DESC, english, chinese; 
+-----------+--------+--------+-------+ 
| name | math | english | chinese | 
+-----------+--------+--------+-------+ | 唐三藏 | 98 | 56 | 67 | 
| 猪悟能 | 98 | 90 | 88 | 
| 刘玄德 | 85 | 45 | 55 | 
| 曹孟德 | 84 | 67 | 82 | 
| 孙悟空 | 78 | 77 | 87 | 
| 孙权 | 73 | 78 | 70 | 
| 宋公明 | 65 | 30 | 75 | 
+-----------+--------+--------+-------+ 
7 rows in set (0.00 sec) 

-- ORDER BY 中可以使用表达式 
 
SELECT name, chinese + english + math FROM exam_result 
 ORDER BY chinese + english + math DESC; 
+-----------+-------------------------+ 
| name | chinese + english + math | 
+-----------+-------------------------+ 
| 猪悟能 | 276 | 
| 孙悟空 | 242 | 
| 曹孟德 | 233 | 
| 唐三藏 | 221 | 
| 孙权 | 221 | 
| 刘玄德 | 185 | 
| 宋公明 | 170 | 
+-----------+-------------------------+ 
7 rows in set (0.00 sec) 

-- ORDER BY 子句中可以使用列别名 
 
SELECT name, chinese + english + math 总分 FROM exam_result 
 ORDER BY 总分 DESC; 
+-----------+--------+ 
| name | 总分 | 
+-----------+--------+ 
| 猪悟能 | 276 | 
| 孙悟空 | 242 | 
| 曹孟德 | 233 | 
| 唐三藏 | 221 | 
| 孙权 | 221 | 
| 刘玄德 | 185 | 
| 宋公明 | 170 | 
+-----------+--------+ 
7 rows in set (0.00 sec) 

-- 结合 WHERE 子句 和 ORDER BY 子句 
 
SELECT name, math FROM exam_result 
 WHERE name LIKE '孙%' OR name LIKE '曹%' 
 ORDER BY math DESC; 
+-----------+--------+ 
| name | math | 
+-----------+--------+ 
| 曹孟德 | 84 | 
| 孙悟空 | 78 | 
| 孙权 | 73 | 
+-----------+--------+ 
3 rows in set (0.00 sec) 

-- 起始下标为 0 
  
-- 从 s 开始，筛选 n 条结果 
SELECT ... FROM table_name [WHERE ...] [ORDER BY ...] LIMIT s, n
-- 从 0 开始，筛选 n 条结果
SELECT ... FROM table_name [WHERE ...] [ORDER BY ...] LIMIT n;
 ; 
 
-- 从 s 开始，筛选 n 条结果，比第二种用法更明确，建议使用 
SELECT ... FROM table_name [WHERE ...] [ORDER BY ...] LIMIT n OFFSET s;

-- 第 1 页 
 
SELECT id, name, math, english, chinese FROM exam_result 
 ORDER BY id LIMIT 3 OFFSET 0; 
+----+-----------+--------+--------+-------+ 
| id | name | math | english | chinese | 
+----+-----------+--------+--------+-------+ 
| 1 | 唐三藏 | 98 | 56 | 67 | 
| 2 | 孙悟空 | 78 | 77 | 87 | 
| 3 | 猪悟能 | 98 | 90 | 88 | 
+----+-----------+--------+--------+-------+ 
3 rows in set (0.02 sec) 

-- 第 2 页 
 
SELECT id, name, math, english, chinese FROM exam_result 
 ORDER BY id LIMIT 3 OFFSET 3; 
+----+-----------+--------+--------+-------+ 
| id | name | math | english | chinese | 
+----+-----------+--------+--------+-------+ 
| 4 | 曹孟德 | 84 | 67 | 82 | 
| 5 | 刘玄德 | 85 | 45 | 55 | 
| 6 | 孙权 | 73 | 78 | 70 | 
+----+-----------+--------+--------+-------+ 
3 rows in set (0.00 sec) 

-- 第 3 页，如果结果不足 3 个，不会有影响 
 
SELECT id, name, math, english, chinese FROM exam_result 
 ORDER BY id LIMIT 3 OFFSET 6; 
+----+-----------+--------+--------+-------+ 
| id | name | math | english | chinese | 
+----+-----------+--------+--------+-------+ 
| 7 | 宋公明 | 65 | 30 | 75 | 
+----+-----------+--------+--------+-------+ 
1 row in set (0.00 sec) 

UPDATE table_name SET column = expr [, column = expr ...] 
 [WHERE ...] [ORDER BY ...] [LIMIT ...] 

-- 更新值为具体值 
 
-- 查看原数据 
SELECT name, math FROM exam_result WHERE name = '孙悟空'; 
+-----------+--------+ 
| name | math | 
+-----------+--------+ 
| 孙悟空 | 78 | 
+-----------+--------+ 
1 row in set (0.00 sec) 
 
-- 数据更新 
UPDATE exam_result SET math = 80 WHERE name = '孙悟空'; 
Query OK, 1 row affected (0.04 sec) 
Rows matched: 1 Changed: 1 Warnings: 0 
 
-- 查看更新后数据 
SELECT name, math FROM exam_result WHERE name = '孙悟空'; 
+-----------+--------+ 
| name | math | 
+-----------+--------+ 
| 孙悟空 | 80 | 
+-----------+--------+ 
1 row in set (0.00 sec) 

-- 一次更新多个列 

-- 查看原数据
SELECT name, math, chinese FROM exam_result WHERE name = '曹孟德';
+-----------+--------+-------+
|  name     |  math  |chinese| 
+-----------+--------+-------+ 
| 曹孟德     | 84     | 82    | 
+-----------+--------+-------+ 
1 row in set (0.00 sec) 
 
-- 数据更新 
UPDATE exam_result SET math = 60, chinese = 70 WHERE name = '曹孟德'; 
Query OK, 1 row affected (0.14 sec) 
Rows matched: 1 Changed: 1 Warnings: 0 
 
-- 查看更新后数据 
SELECT name, math, chinese FROM exam_result WHERE name = '曹孟德'; 
+-----------+--------+-------+ 
| name | math | chinese | 
+-----------+--------+-------+ 
| 曹孟德 | 60 | 70 | 
+-----------+--------+-------+ 
1 row in set (0.00 sec) 

-- 更新值为原值基础上变更 
 
-- 查看原数据 
-- 别名可以在ORDER BY中使用 
SELECT name, math, chinese + math + english 总分 FROM exam_result 
 ORDER BY 总分 LIMIT 3; 
+-----------+--------+--------+ 
| name | math | 总分 | 
+-----------+--------+--------+ 
| 宋公明 | 65 | 170 | 
| 刘玄德 | 85 | 185 | 
| 曹孟德 | 60 | 197 | 
+-----------+--------+--------+ 
3 rows in set (0.00 sec) 
 
-- 数据更新，不支持 math += 30 这种语法 
UPDATE exam_result SET math = math + 30 
 ORDER BY chinese + math + english LIMIT 3; 
 
-- 查看更新后数据 
-- 思考：这里还可以按总分升序排序取前 3 个么？ 
SELECT name, math, chinese + math + english 总分 FROM exam_result 
 WHERE name IN ('宋公明', '刘玄德', '曹孟德'); 
+-----------+--------+--------+ 
| name | math | 总分 | 
+-----------+--------+--------+ 
| 曹孟德 | 90 | 227 | 
| 刘玄德 | 115 | 215 | 
| 宋公明 | 95 | 200 | 
+-----------+--------+--------+ 
3 rows in set (0.00 sec) 
 
-- 按总成绩排序后查询结果 
SELECT name, math, chinese + math + english 总分 FROM exam_result 
 ORDER BY 总分 LIMIT 3; 
+-----------+--------+--------+ 
| name | math | 总分 | 
+-----------+--------+--------+ 
| 宋公明 | 95 | 200 | 
| 刘玄德 | 115 | 215 | 
| 唐三藏 | 98 | 221 | 
+-----------+--------+--------+ 
3 rows in set (0.00 sec) 

-- 没有 WHERE 子句，则更新全表 
 
-- 查看原数据 
SELECT * FROM exam_result; 
+----+-----------+-------+--------+--------+ 
| id | name | chinese | math | english | 
+----+-----------+-------+--------+--------+ 
| 1 | 唐三藏 | 67 | 98 | 56 | 
| 2 | 孙悟空 | 87 | 80 | 77 | 
| 3 | 猪悟能 | 88 | 98 | 90 | 
| 4 | 曹孟德 | 70 | 90 | 67 | 
| 5 | 刘玄德 | 55 | 115 | 45 | 
| 6 | 孙权 | 70 | 73 | 78 | 
| 7 | 宋公明 | 75 | 95 | 30 | 
+----+-----------+-------+--------+--------+ 
7 rows in set (0.00 sec)
-- 数据更新 
UPDATE exam_result SET chinese = chinese * 2; 
Query OK, 7 rows affected (0.00 sec) 
Rows matched: 7 Changed: 7 Warnings: 0 
 
-- 查看更新后数据 
SELECT * FROM exam_result; 
+----+-----------+-------+--------+--------+ 
| id | name | chinese | math | english | 
+----+-----------+-------+--------+--------+ 
| 1 | 唐三藏 | 134 | 98 | 56 | 
| 2 | 孙悟空 | 174 | 80 | 77 | 
| 3 | 猪悟能 | 176 | 98 | 90 | 
| 4 | 曹孟德 | 140 | 90 | 67 | 
| 5 | 刘玄德 | 110 | 115 | 45 | 
| 6 | 孙权 | 140 | 73 | 78 | 
| 7 | 宋公明 | 150 | 95 | 30 | 
+----+-----------+-------+--------+--------+ 
7 rows in set (0.00 sec)

DELETE FROM table_name [WHERE ...] [ORDER BY ...] [LIMIT ...] 

-- 查看原数据 
SELECT * FROM exam_result WHERE name = '孙悟空'; 
+----+-----------+-------+--------+--------+ 
| id | name | chinese | math | english | 
+----+-----------+-------+--------+--------+ 
| 2 | 孙悟空 | 174 | 80 | 77 | 
+----+-----------+-------+--------+--------+ 
1 row in set (0.00 sec) 
 
-- 删除数据 
DELETE FROM exam_result WHERE name = '孙悟空'; 
Query OK, 1 row affected (0.17 sec) 
 
-- 查看删除结果 
SELECT * FROM exam_result WHERE name = '孙悟空'; 
Empty set (0.00 sec)

-- 准备测试表 
CREATE TABLE for_delete ( 
 id INT PRIMARY KEY AUTO_INCREMENT, 
 name VARCHAR(20) 
); 
Query OK, 0 rows affected (0.16 sec) 
 
-- 插入测试数据 
INSERT INTO for_delete (name) VALUES ('A'), ('B'), ('C'); 
Query OK, 3 rows affected (1.05 sec) 
Records: 3 Duplicates: 0 Warnings: 0 
 
-- 查看测试数据 
SELECT * FROM for_delete; 
+----+------+ 
| id | name | 
+----+------+ 
| 1 | A | 
| 2 | B | 
| 3 | C | 
+----+------+ 
3 rows in set (0.00 sec) 

-- 删除整表数据 
 
DELETE FROM for_delete; 
Query OK, 3 rows affected (0.00 sec) 
 
-- 查看删除结果 
SELECT * FROM for_delete; 
Empty set (0.00 sec) 

-- 再插入一条数据，自增 id 在原值上增长 
INSERT INTO for_delete (name) VALUES ('D'); 
Query OK, 1 row affected (0.00 sec) 
 
-- 查看数据 
SELECT * FROM for_delete; 
+----+------+ 
| id | name | 
+----+------+ 
| 4 | D | 
+----+------+ 
1 row in set (0.00 sec) 
 
-- 查看表结构，会有 AUTO_INCREMENT=n 项 
SHOW CREATE TABLE for_delete\G 
*************************** 1. row *************************** 
 Table: for_delete 
Create Table: CREATE TABLE `for_delete` ( 
 `id` int(11) NOT NULL AUTO_INCREMENT, 
 `name` varchar(20) DEFAULT NULL, 
  PRIMARY KEY (`id`) 
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8 
1 row in set (0.00 sec) 

TRUNCATE [TABLE] table_name

-- 准备测试表 
CREATE TABLE for_truncate ( 
 id INT PRIMARY KEY AUTO_INCREMENT, 
 name VARCHAR(20) 
); 
Query OK, 0 rows affected (0.16 sec) 
 
-- 插入测试数据 
INSERT INTO for_truncate (name) VALUES ('A'), ('B'), ('C'); 
Query OK, 3 rows affected (1.05 sec) 
Records: 3 Duplicates: 0 Warnings: 0 
 
-- 查看测试数据 
SELECT * FROM for_truncate; 
+----+------+ 
| id | name | 
+----+------+ 
| 1 | A | 
| 2 | B | 
| 3 | C | 
+----+------+ 
3 rows in set (0.00 sec) 

-- 截断整表数据，注意影响行数是 0，所以实际上没有对数据真正操作 
TRUNCATE for_truncate; 
Query OK, 0 rows affected (0.10 sec) 
 
-- 查看删除结果 
SELECT * FROM for_truncate; 
Empty set (0.00 sec) 

-- 再插入一条数据，自增 id 在重新增长 
INSERT INTO for_truncate (name) VALUES ('D'); 
Query OK, 1 row affected (0.00 sec)  
-- 查看数据 
SELECT * FROM for_truncate; 
+----+------+ 
| id | name | 
+----+------+ 
| 1 | D | 
+----+------+ 
1 row in set (0.00 sec) 
 
-- 查看表结构，会有 AUTO_INCREMENT=2 项 
SHOW CREATE TABLE for_truncate\G 
*************************** 1. row *************************** 
 Table: for_truncate 
Create Table: CREATE TABLE `for_truncate` ( 
 `id` int(11) NOT NULL AUTO_INCREMENT, 
 `name` varchar(20) DEFAULT NULL, 
 PRIMARY KEY (`id`) 
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8 
1 row in set (0.00 sec) 

INSERT INTO table_name [(column [, column ...])] SELECT ... 

-- 创建原数据表 
 
CREATE TABLE duplicate_table (id int, name varchar(20)); 
Query OK, 0 rows affected (0.01 sec) 
 
-- 插入测试数据 
INSERT INTO duplicate_table VALUES 
 (100, 'aaa'), 
 (100, 'aaa'), 
 (200, 'bbb'), 
 (200, 'bbb'), 
 (200, 'bbb'), 
 (300, 'ccc'); 
Query OK, 6 rows affected (0.00 sec) 
Records: 6 Duplicates: 0 Warnings: 0 

-- 创建一张空表 no_duplicate_table，结构和 duplicate_table 一样 
CREATE TABLE no_duplicate_table LIKE duplicate_table; 
Query OK, 0 rows affected (0.00 sec) 
-- 将 duplicate_table 的去重数据插入到 no_duplicate_table 
INSERT INTO no_duplicate_table SELECT DISTINCT * FROM duplicate_table; 
Query OK, 3 rows affected (0.00 sec) 
Records: 3 Duplicates: 0 Warnings: 0 
 
-- 通过重命名表，实现原子的去重操作 
RENAME TABLE duplicate_table TO old_duplicate_table, 
 no_duplicate_table TO duplicate_table; 
Query OK, 0 rows affected (0.00 sec) 
 
-- 查看最终结果 
SELECT * FROM duplicate_table; 
+------+------+ 
| id | name | 
+------+------+ 
| 100 | aaa | 
| 200 | bbb | 
| 300 | ccc | 
+------+------+ 
3 rows in set (0.00 sec) 

-- 使用 * 做统计，不受 NULL 影响 
 
SELECT COUNT(*) FROM students; 
+----------+ 
| COUNT(*) | 
+----------+ 
| 4 | 
+----------+ 
1 row in set (0.00 sec) 
 
-- 使用表达式做统计 
 
SELECT COUNT(1) FROM students; 
| COUNT(1) |
+----------+
| 4 |
+----------+
1 row in set (0.00 sec)

-- NULL 不会计入结果
SELECT COUNT(qq) FROM students;
+-----------+
| COUNT(qq) |
+-----------+
| 1 |
+-----------+
1 row in set (0.00 sec)

-- COUNT(math) 统计的是全部成绩
SELECT COUNT(math) FROM exam_result;
+---------------+
| COUNT(math) |
+---------------+
| 6 |
+---------------+
1 row in set (0.00 sec)

-- COUNT(DISTINCT math) 统计的是去重成绩数量
SELECT COUNT(DISTINCT math) FROM exam_result;
+------------------------+
| COUNT(DISTINCT math) |
+------------------------+
|        5               |
+------------------------+
1 row in set (0.00 sec)

SELECT SUM(math) FROM exam_result;
+-------------+
| SUM(math) |
+-------------+
| 569 |
+-------------+
1 row in set (0.00 sec)
-- 不及格 < 60 的总分，没有结果，返回 NULL
SELECT SUM(math) FROM exam_result WHERE math < 60;
+-------------+
| SUM(math) |
+-------------+
| NULL |
+-------------+
1 row in set (0.00 sec)

SELECT AVG(chinese + math + english) 平均总分 FROM exam_result;
+--------------+
| 平均总分 |
+--------------+
| 297.5 |
+--------------+

SELECT MAX(english) FROM exam_result;
+-------------+
| MAX(english) |
+-------------+
| 90 |
+-------------+
1 row in set (0.00 sec)

SELECT MIN(math) FROM exam_result WHERE math > 70;
+-------------+
| MIN(math) |
+-------------+
| 73 |
+-------------+
1 row in set (0.00 sec)

select column1, column2, .. from table group by column;

select deptno,avg(sal),max(sal) from EMP group by deptno;

select avg(sal),min(sal),job, deptno from EMP group by deptno, job;

select avg(sal) from EMP group by deptno

select avg(sal) as myavg from EMP group by deptno having myavg<2000;

--having经常和group by搭配使用，作用是对分组进行筛选，作用有些像where。