OCP-1Z0-051-V9.02-137题
137. View the Exhibits and examine PRODUCTS and SALES tables.
You issue the following query to display product name and the number of times the product has been
sold:
SQL>SELECT p.prod_name, i.item_cnt
FROM (SELECT prod_id, COUNT(*) item_cnt
FROM sales
GROUP BY prod_id) i RIGHT OUTER JOIN products p
ON i.prod_id = p.prod_id;
What happens when the above statement is executed?
A. The statement executes successfully and produces the required output.
B. The statement produces an error because ITEM_CNT cannot be displayed in the outer query.
C. The statement produces an error because a subquery in the FROM clause and outer-joins cannot be
used together.
D. The statement produces an error because the GROUP BY clause cannot be used in a subquery in the
FROM clause.
Answer: A
答案解析：
通过子查询，查询出产品卖出去的次数。
在通过右连接产品表，显示出所有产品。
实验验证：
sh@TEST0924> SELECT p.prod_name, i.item_cnt
2 FROM (SELECT prod_id, COUNT(*) item_cnt FROM sales GROUP BY prod_id)
3 i RIGHT OUTER JOIN products p
4 ON i.prod_id = p.prod_id;
PROD_NAME ITEM_CNT
-------------------------------------------------- ----------
Envoy External Keyboard 3441
SIMM- 8MB PCMCIAII card 19557
Mouse Pad 29282
External 6X CD-ROM 13043
...
72 rows selected.