内部联接-使用任一等效查询的内部联接给出两个表的交集，即它们共有的两行.
左外连接- 左外部联接将给出A中的所有行，以及B中的所有常见行.
完全外部联接- 完整的外部联接将为您提供A和B的并集，即A中的所有行和B中的所有行.如果A中的某物在B中没有对应的基准，则B部分为空，反之反之亦然. 检查此

Inner join - An inner join using either of the equivalent queries gives the intersection of the two tables, i.e. the two rows they have in common.
Left outer join - A left outer join will give all rows in A, plus any common rows in B.
Full outer join - A full outer join will give you the union of A and B, i.e. All the rows in A and all the rows in B. If something in A doesn't have a corresponding datum in B, then the B portion is null, and vice versa. check this