常见SQL关联查询

1. inner join 内连接查询

SELECT a.*,b.* FROM table_a a INNER JOIN table_b b ON a.id=b.id；

2. left join 左关联查询

SELECT a.*,b.* FROM table_a a LEFT JOIN table_b b ON a.id=b.id；

3.right join 右关联查询

SELECT a.*,b.* FROM table_a a RIGHT JOIN table_b b ON a.id=b.id；

4.左连接-内连接

SELECT a.*,b.* FROM table_a a LEFT JOIN table_b b ON a.id=b.id WHERE b.id IS NULL；

5. 右连接-内连接

SELECT a.*,b.* FROM table_a a RIGHT JOIN table_b b ON a.id=b.id WHERE a.id IS NULL