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Re: Relational query question






On 29/09/15 13:01, Richard Reina wrote:
If I have three simple tables:

mysql> select * from customer;
+----+--------+
| ID | NAME   |
+----+--------+
|  1 | Joey   |
|  2 | Mike   |
|  3 | Kellie |
+----+--------+
3 rows in set (0.00 sec)

mysql> select * from fruit;
+----+---------+
| ID | NAME    |
+----+---------+
|  1 | Apples  |
|  2 | Grapes  |
|  3 | Oranges |
|  4 | Kiwis   |
+----+---------+
4 rows in set (0.00 sec)

mysql> select * from purchases;
+----+---------+----------+
| ID | CUST_ID | FRUIT_ID |
+----+---------+----------+----
|  2 |          3 |           2       |
|  3 |          1 |           4       |
|  4 |          1 |           2       |
|  5 |          2 |           1       |
+----+---------+----------+----

I am having trouble understanding a relational query. How can I select
those fruits that Joey has not purchased?


I think you are going to want to use a "LEFT JOIN" using "purchases" as the common table to join with a WHERE purchases.FRUIT_ID IS NULL



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