mysql的内连接，外连接（左外连接，右外连接）巩固

1 select a.goods_id,a.goods_name,b.cate_name
2 from tdb_goods a,tdb_goods_cate b
3 where a.cate_id = b.cate_id;
4 
5 《==============上下两种写法等价===============》
6 
7 select c.goods_id,c.goods_name,d.cate_name
8 from tdb_goods c INNER JOIN tdb_goods_cate d
9 on c.cate_id = d.cate_id;

1 select c.goods_id,c.goods_name,d.cate_name
2 from tdb_goods c LEFT JOIN tdb_goods_cate d
3 on c.cate_id = d.cate_id;
4 
5 
6 select c.goods_id,c.goods_name,d.cate_name
7 from tdb_goods c RIGHT JOIN tdb_goods_cate d
8 on c.cate_id = d.cate_id;