mysql內聯結、左聯結、右聯結

標籤：

--內聯結----select goods_id,goods_name,cate_name from tdb_goods inner join tdb_goods_cates on tdb_goods.cate_id=tdb_goods_cates.cate_id\G; 內聯結返回兩張表中都有的select goods_id,goods_name,brand_name from tdb_goods inner join tdb_brand on tdb_goods.brand_id=tdb_brand.brand_id;--左串連--select goods_id,goods_name,cate_name from tdb_goods left join tdb_goods_cates on tdb_goods.cate_id=tdb_goods_cates.cate_id\G; 左聯結返回第一張（即左邊）表中都有的select goods_id,goods_name,brand_name from tdb_goods left join tdb_brand on tdb_goods.brand_id=tdb_brand.brand_id;             所參照右表沒有的值用null代替--右串連--select goods_id,goods_name,cate_name from tdb_goods right join tdb_goods_cates on tdb_goods.cate_id=tdb_goods_cates.cate_id\G; 右聯結返回第二張（即右邊）表中都有的select goods_id,goods_name,brand_name from tdb_goods right join tdb_brand on tdb_goods.brand_id=tdb_brand.brand_id;             所參照左表沒有的值用null代替對照：select goods_id,goods_name,brand_name from tdb_brand left join tdb_goods on tdb_goods.brand_id=tdb_brand.brand_id;總結：內聯結只會顯示兩張表中都有的列，左串連參照左表，右表中無值就設null，右串連參照右表，左表無值就設null，左右串連可互換表名結果相同。

 

mysql內聯結、左聯結、右聯結