Atchaya's Check Your Oracle Knowledge

Examine the description of the STUDENTS table: STD_ID NUMBER(4) COURSE_ID VARCHARD2(10) START_DATE DATE END_DATE DATE Which two aggregate functions are valid on the START_DATE column? (Choose two) A. SUM(start_date) B. AVG(start_date) C. COUNT(start_date) D. AVG(start_date, end_date) E. MIN(start_date) F. MAXIMUM(start_date) Answer: C & E Explanation: It is possible to apply COUNT() and MIN() functions on the column with DATE data type. Incorrect Answers A: Function SUM() cannot be used with DATE data type column. B: Function AVG() cannot be used with DATE data type column. D: Function AVG() cannot be used with DATE data type column, and function AVG() just has one parameter X, not two. It averages all X column values returned by the SELECT statement. F: There is no MAXIMUM() function in Oracle, only MAX() function exists.

Examine the description of the EMPLOYEES table: EMP_ID NUMBER(4) NOT NULL LAST_NAME VARCHAR2(30) NOT NULL FIRST_NAME VARCHAR2(30) DEPT_ID NUMBER(2) JOB_CAT VARCHARD2(30) SALARY NUMBER(8,2) Which statement shows the maximum salary paid in each job category of each department? A.SELECT dept_id, job_cat, MAX(salary) FROM employees WHERE salary > MAX(salary); B.SELECT dept_id, job_cat, MAX(salary) FROM employees GROUP BY dept_id, job_cat; C. SELECT dept_id, job_cat, MAX(salary) FROM employees; D. SELECT dept_id, job_cat, MAX(salary) FROM employees GROUP BY dept_id; Answer: B Explanation: This answer provides correct syntax and semantics to show the maximum salary paid in each job category of each department. Incorrect Answers A: This query will not return any row because condition SALARY > MAX(SALARY) is FALSE. C: This query will return error because you cannot show maximum salary with DEPT_ID and JOB_CAT without grouping by these columns. D: The GROUP BY clause is missing JOB_ID col

You are sorting data in a table in you SELECT statement in descending order. The column you are sorting on contains NULL records, where will the NULL record appears? A.At the beginning of the list. B.At the end of the list. C.In the middle of the list. D.At the same location they are listed in the unordered table. Answer: A Explanation: When sorting a column with null values in ascending order then the oracle places the Null values at the end of the list if the sorting is in descending order the oracle places the null values at the start of the list.