Pass 1z0-071 Exam Guide

In SQL, the correct usage of conversion functions is crucial when performing operations on dates. Oracle uses the TO_DATE function to convert a string to a date, and the TO_CHAR function to convert dates or numbers to strings.

Statement C is correct: WHERE order_date > TO_DATE('JUL 10 2018','MON DD YYYY'); is a proper use of the TO_DATE function. It converts the string 'JUL 10 2018' to a date type, with the format 'MON DD YYYY', which is then used to compare with the order_date.

Statements A, B, D, and E are incorrect or misuse conversion functions:

A is incorrect because TO_CHAR is used to convert dates or numbers to strings, not the other way around, and therefore should not be compared with order_date.

B is incorrect because order_date is of type DATE, and you should not compare a DATE with a string without converting it; the TO_CHAR here should be TO_DATE.

D is incorrect because it mixes TO_DATE and TO_CHAR in the same IN list, which should contain date types only.

E is incorrect because TO_DATE should take a string as an argument, not a date returned by ADD_MONTHS.

To format a date in Oracle SQL, TO_CHAR function is used to convert date types to string with a specified format:

Option A: SELECT TO_CHAR(SYSDATE, 'FMDAY, DD MONTH, YYYY') FROM DUAL;

This correctly applies the date format model 'FMDAY, DD MONTH, YYYY', which will display the date as requested: "MONDAY, 21 MAY, 2019". FM modifier is used to remove padding blanks or leading zeros.

Options B, C, and D do not achieve the desired output:

Option B is incorrect because TO_DATE converts a string to a date, not format a date.

Option C and D have incorrect format strings that do not match the required output format.

The correct way to compute the total annual compensation, which includes the monthly salary and the monthly commission (if any), is:

Option C: SELECT last_name, (monthly_salary * 12) + (monthly_salary * 12 * NVL(monthly_commission_pct, 0)) AS annual_comp FROM employees;

This statement takes the monthly salary and multiplies it by 12 to get the annual salary, and then adds the annual commission which is the monthly salary multiplied by the commission percentage (if any, else 0) and then by 12.

Options A, B, and D are incorrect because:

Option A: Does not handle the case where the commission percentage is NULL which would result in NULL for the entire expression when added to the monthly salary.

Option B: Does not consider that the commission percentage might be NULL which could lead to incorrect calculations (or NULL values if commission is NULL).

Option D: Incorrectly adds the monthly commission percentage directly to the annual salary without considering that the percentage needs to be applied to the salary.

When comparing the performance of different SQL join types and conditions, Oracle SQL optimizations generally ensure that performance is consistent across different syntactical forms of expressing the same logic:

Option A: False. The BETWEEN condition does not inherently perform worse than using >= and <=. Oracle's optimizer typically evaluates these conditions similarly, optimizing the underlying execution based on the data distribution and available indexes.

Option B: False. Oracle's optimizer is designed to handle both Oracle-specific join syntax and ANSI join syntax with equal competence. Performance differences would typically be negligible because the optimizer translates both into an optimal execution plan based on the same underlying mechanisms.

Option C: True. The join syntax used (whether Oracle's traditional syntax or ANSI standard syntax) generally does not affect the performance. Oracle's query optimizer is adept at translating different syntaxes into efficient execution plans.

Option D: False. The assertion that BETWEEN always performs better than >= and <= is incorrect. Performance depends more on factors like indexing, the specific data and distribution, and the Oracle optimizer's capabilities than on the mere choice of syntax.

Option E: False. While table aliases help improve query readability and can prevent ambiguity in SQL queries, they do not inherently improve performance. Their use is a best practice for code clarity and maintenance, not performance enhancement.