标准SQL语法：
1、SELECT 语句 - 从表中检索数据
SELECT column1, column2, ...
FROM table_name
WHERE condition;
-- 示例：从名为"students"的表中选择所有年龄大于20的学生
SELECT name, age
FROM students
WHERE age > 20;2、INSERT INTO 语句 - 向表中插入新数据
INSERT INTO table_name (column1, column2, ...)
VALUES (value1, value2, ...);
-- 示例：向"students"表中插入一条新记录
INSERT INTO students (name, age, grade)
VALUES ('张三', 22, '三年级');3、UPDATE 语句 - 更新表中的数据
UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;
-- 示例：将名为"张三"的学生的年龄更新为23
UPDATE students
SET age = 23
WHERE name = '张三';4、DELETE 语句 - 从表中删除数据
DELETE FROM table_name
WHERE condition;
-- 示例：删除所有年龄小于20的学生
DELETE FROM students
WHERE age < 20;5、CREATE TABLE 语句 - 创建一个新表
CREATE TABLE table_name (
column1 datatype,
column2 datatype,
...
);
-- 示例：创建一个名为"courses"的表
CREATE TABLE courses (
id INT PRIMARY KEY,
course_name VARCHAR(255) NOT NULL,
teacher_name VARCHAR(255)
);6、ALTER TABLE 语句 - 修改表结构（例如，添加、删除或修改列）
-- 示例：向"courses"表添加一个名为"credits"的列
ALTER TABLE courses
ADD credits INT;
-- 示例：从"courses"表中删除名为"teacher_name"的列
ALTER TABLE courses
DROP COLUMN teacher_name;7、DROP TABLE 语句 - 删除表
DROP TABLE table_name;
-- 示例：删除名为"courses"的表
DROP TABLE courses;8、SELECT ... ORDER BY 语句 - 对结果集进行排序
SELECT column1, column2, ...
FROM table_name
ORDER BY column1, column2, ... ASC|DESC;
-- 示例：从"students"表中选择所有学生，并按年龄升序排序
SELECT * FROM students
ORDER BY age ASC;9、SELECT ... GROUP BY 语句 - 结合聚合函数，按一个或多个列对结果集进行分组
SELECT column_name(s), aggregate_function(column_name)
FROM table_name
WHERE condition
GROUP BY column_name(s);
-- 示例：计算每个年级的学生数量
SELECT grade, COUNT(*) as student_count
FROM students
GROUP BY grade;10、SELECT ... JOIN 语句 - 从两个或多个表中检索数据
SELECT columns
FROM table1
JOIN table2
ON table1.column_name = table2.column_name;
-- 示例：从"students"和"courses"表中检索学生的姓名和他们所选的课程名称（假设有一个连接表）
SELECT students.name, courses.course_name
FROM students
JOIN enrollment ON students.id = enrollment.student_id
JOIN courses ON enrollment.course_id = courses.id;
