如何重复使用同一细节表上的内连接

Question

我正在尝试使用TWICE内部连接语句来获取相同详细信息表中的引用值。

Master table: bags_tbl
ID ...     bagA        bagB 
1  ...     121         122 
2  ...     123         124 
3  ...     125         126

Detail table: fruit_tbl
ID ...     fruit  ... 
121        strawbery 
122        apple
123        orange 
124        raspberry
125        pear 
126        pineapple


SELECT
bags_tbl.ID,
bags_tbl.A,
bags_tbl.B,
fruit_tbl.fruit AS bagA_fruit,
fruit_tbl.fruit AS bagB_fruit
FROM
bags_tbl
Inner Join fruit_tbl ON bags_tbl.bagA = fruit_tbl.fruit
Inner Join fruit_tbl ON bags_tbl.bagB = fruit_tbl.fruit

这个抛出错误：没有唯一的表/别名...... 如何使SQL语句获取主表的文本表示？

非常感谢

Answer 1

SELECT
    bags_tbl.ID,
    bags_tbl.A,
    bags_tbl.B,
    A.fruit AS bagA_fruit,
    B.fruit AS bagB_fruit
FROM bags_tbl
Inner Join fruit_tbl A ON bags_tbl.bagA = A.id
Inner Join fruit_tbl B ON bags_tbl.bagB = B.id

Answer 2

试试这个。您需要为每个连接授予一个唯一的别名，以便SQL知道您在SELECT子句中引用了哪一个。

SELECT
bags_tbl.ID,
bags_tbl.A,
bags_tbl.B,
fruitA.fruit AS bagA_fruit,
fruitB.fruit AS bagB_fruit
FROM
bags_tbl
JOIN fruit_tbl fruitA ON bags_tbl.bagA = fruitA.id
JOIN fruit_tbl fruitB ON bags_tbl.bagB = fruitB.id