OCP-1Z0-051-2015-6题

QUESTION NO: 6

See the Exhibit and examine the structure of the CUSTOMERS table:



Using the CUSTOMERS table, you need to generate a report that shown the average credit limit

for customers in WASHINGTON and NEW YORK.

Which SQL statement would produce the required result?

A.

SELECT cust_city, AVG(cust_credit_limit)

FROM customers

WHERE cust_city IN ('WASHINGTON','NEW YORK')

GROUP BY cust_credit_limit, cust_city;

B.

SELECT cust_city, AVG(cust_credit_limit)

FROM customers

WHERE cust_city IN ('WASHINGTON','NEW YORK')

GROUP BY cust_city,cust_credit_limit;

C.

SELECT cust_city, AVG(cust_credit_limit)

FROM customers

WHERE cust_city IN ('WASHINGTON','NEW YORK')

GROUP BY cust_city;

D.

SELECT cust_city, AVG(NVL(cust_credit_limit,0))

FROM customers

WHERE cust_city IN ('WASHINGTON','NEW YORK');

Answer:C

Explanation:

Creating Groups of Data: GROUP BY Clause Syntax

You can use the GROUP BY clause to divide the rows in a table into groups. You can then use the

group functions to return summary information for each group.

In the syntax:

group_by_expression Specifies the columns whose values determine the basis for grouping rows

Guidelines

• If you include a group function in a SELECT clause, you cannot select individual results as well,

unless the individual column appears in the GROUP BY clause. You receive an error message if

you fail to include the column list in the GROUP BY clause.

• Using a WHERE clause, you can exclude rows before dividing them into groups.

• You must include the columns in the GROUP BY clause.
• You cannot use a column alias in the GROUP BY clause.

用group by 分句注意几点

如果你要在select语句中包含分组方法，在查询个别列结果时要在group by子句中出现个别列。

group by 子句必须包含列

列别名不能出现在group by 子句中；