单项选择题
A. SELECT TO_CHAR(SYSDATE,'yyyy') FROM dual;
B. SELECT TO_DATE(SYSDATE,'yyyy') FROM dual;
C. SELECT DECODE(SUBSTR(SYSDATE, 8), 'YYYY') FROM dual;
D. SELECT DECODE(SUBSTR(SYSDATE, 8), 'year') FROM dual;
E. SELECT TO_CHAR(SUBSTR(SYSDATE, 8,2),'yyyy') FROM dual;
单项选择题 The EMPLOYEES table contains these columns: LAST_NAME VARCHAR2 (25) SALARY NUMBER (6,2) COMMISSION_PCT NUMBER (6) You need to write a query that will produce these results: 1. Display the salary multiplied by the commission_pct. 2. Exclude employees with a zero commission_pct. 3. Display a zero for employees with a null commission value. Evaluate the SQL statement: SELECT LAST_NAME, SALARY*COMMISSION_PCT FROM EMPLOYEES WHERE COMMISSION_PCT IS NOT NULL; What does the statement provide? （）
单项选择题 A subquery can be used to （）.
单项选择题 Which clause should you use to exclude group results? （）