MySQL - 2、数据操作

0、创建测试表：

CREATE TABLE students (
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(50) NOT NULL,
    age INT,
    score FLOAT
);

1、INSERT 插入数据：

INSERT INTO students (name, age, score) VALUES
    ('lfsun1', 25, 85.5),
    ('lfsun2', 22, 78.3),
    ('lfsun3', 27, 92.1),
    ('lfsun4', 23, 68.9);
    

2、SELECT 查询数据：

-- 查询所有学生信息
SELECT * FROM students;

-- 查询年龄大于等于25岁的学生
SELECT * FROM students WHERE age >= 25;

-- 查询分数最高的学生
SELECT * FROM students ORDER BY score DESC LIMIT 1;

3、UPDATE 更新数据：

-- 将id为3的学生分数更新为95.2
UPDATE students SET score = 95.2 WHERE id = 3;

5、DELETE 删除数据：

-- 删除年龄小于等于22岁的学生
DELETE FROM students WHERE age <= 22;

6、REPLACE 替换数据（只适用于有唯一索引或主键的表）：

-- 假设id为1的学生信息已经存在，则替换为新的数据，否则插入新的数据
REPLACE INTO students (id, name, age, score) VALUES (2, 'lfsun-1', 21, 88.7);

7、LOAD DATA INFILE 从外部文件导入数据：

假设有一个名为data.csv的CSV文件，包含以下内容：

lfsun-5,21,88.7
lfsun-6,21,88.7
lfsun-7,27,95.2
lfsun-8,23,68.9

– 将data.csv文件中的数据导入到students表中

LOAD DATA INFILE 'data.csv的路径'
INTO TABLE students
FIELDS TERMINATED BY ',' ENCLOSED BY '"'
LINES TERMINATED BY '\n'
(name, age, score);

1、The MySQL server is running with the --secure-file-priv option so it cannot execute this statement 问题解决
2、Loading local data is disabled; this must be enabled on both the client and server sides 问题解决

8、SELECT INTO OUTFILE 将查询结果导出到外部文件：

-- 将所有学生的信息导出到students.csv文件中
SELECT * FROM students
INTO OUTFILE 'students.csv的保存路径'
FIELDS TERMINATED BY ',' ENCLOSED BY '"'
LINES TERMINATED BY '\n';

1、The MySQL server is running with the --secure-file-priv option so it cannot execute this statement 问题解决

9、INSERT INTO SELECT 从一个表中查询数据并插入到另一个表中：

-- 创建mature_students，其结构与students完全相同
CREATE TABLE mature_students LIKE students;
-- 将年龄大于等于25岁的学生的信息插入到mature_students表中
INSERT INTO mature_students (name, age, score)
SELECT name, age, score FROM students WHERE age >= 25;

执行修改数据的SQL语句时，请务必谨慎操作，确保备份数据以防止意外修改或删除。