几张图解释它们之间的区别

1、inner join

用法：

SELECT column_name(s)
FROM table1
JOIN table2
ON table1.column_name=table2.column_name;

2、left join

用法：

SELECT column_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name=table2.column_name;

3、right join

用法：

SELECT column_name(s)
FROM table1
RIGHT JOIN table2
ON table1.column_name=table2.column_name;

4、full outer join

用法：

SELECT column_name(s)
FROM table1
FULL OUTER JOIN table2
ON table1.column_name=table2.column_name;

其他注意事项

• laravel 中默认join为inner join

参考网站

• w3cschool SQL Joins