2023-07-18 15:12
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秒级时间戳：
```
SELECT UNIX_TIMESTAMP();
```
毫秒级时间戳：
```
SELECT UNIX_TIMESTAMP(NOW()) * 1000;
```
2023-07-18 15:11
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1、使用MySQL命令行客户端：
可以使用source命令实现，将多个.sql文件导入到一个MySQL数据库中：
```
mysql> source /path/to/file1.sql;
mysql> source /path/to/file2.sql;
```
2、使用Windows的CMD命令行：
可以使用mysql.exe命令：
```
C:\
2023-07-18 15:09
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```
SELECT student.name,student.age FROM student;
```
2023-07-18 15:08
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```
SELECT * FROM student WHERE student_id IN (SELECT student_id FROM elective GROUP BY student_id HAVING COUNT(*) = (SELECT COUNT(*) FROM course));
```
2023-07-17 09:50
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SELECT * FROM students WHERE MONTH(birth) = MONTH(NOW())
2023-07-16 09:34
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UNION：求两个或多个集合的并集，去除重复
UNION ALL：求两个或多个集合的并集，不去除重复
INTERSECT：求两个或多个集合的交集，去除重复
MINUS：求两个或多个集合的差集，去除重复
2023-07-16 09:34
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SELECT * FROM student WHERE MONTH(birthday) = MONTH(DATE_ADD(NOW(), INTERVAL 1 MONTH));
2023-07-16 09:34
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select distinct student_id
from student_course
group by student_id
having count(*) >= 2;