OCP 1Z0 051 QUESTION NO: 4

QUESTION NO: 4

See the Exhibit and examine the structure and data in the INVOICE table:

Exhibit:



Which two SQL statements would executes successfully? (Choose two.)

A. SELECT MAX(inv_date),MIN(cust_id) FROM invoice;

B. SELECT MAX(AVG(SYSDATE - inv_date)) FROM invoice;

C. SELECT AVG(inv_date) FROM invoice;

D. SELECT AVG(inv_date - SYSDATE),AVG(inv_amt) FROM invoice;

A D 没错，对所有数据聚合。date不能取平均值，但inv_date - sysdate的结果是number，所以可以用avg

TEST > SELECT MAX(inv_date),MIN(cust_id) FROM invoice;
MAX(INV_DATE) MIN(CUST_ID)
------------- ------------
2007-10-01    A1Q
1 row selected

TEST > SELECT AVG(inv_date - SYSDATE),AVG(inv_amt) FROM invoice;
AVG(INV_DATE-SYSDATE) AVG(INV_AMT)
--------------------- ------------
-2578.36114583333         2000
1 row selected

B 同一级别，聚合函数不参嵌套

TEST > SELECT MAX(AVG(SYSDATE - inv_date)) FROM invoice;
SELECT MAX(AVG(SYSDATE - inv_date)) FROM invoice
ORA-00978: nested group function without GROUP BY

TEST > SELECT MAX(AVG(SYSDATE - inv_date)) FROM invoice group by cust_id;
MAX(AVG(SYSDATE-INV_DATE))
--------------------------
2678.69530092593
1 row selected

C date不能取平均值，只有数字可以取平均值

TEST > SELECT AVG(inv_date) FROM invoice;
SELECT AVG(inv_date) FROM invoice
ORA-00932: inconsistent datatypes: expected NUMBER got DATE

Answer: A,D