1z0-071 Premium Exam Questions

The LOCALTIMESTAMP function in Oracle Database returns the current date and time in the session time zone. Given that the session time zone was set to -5:00 with the ALTER SESSION SET TIME_ZONE command, LOCALTIMESTAMP will return the date and time adjusted to this session time zone.

The SYSDATE function, on the other hand, returns the current date and time from the operating system of the database server, which is not affected by the session time zone setting. In the result shown, SYSDATE returns 11-JUL-2019 11:00:00, which reflects the system time zone, not the session time zone.

The time difference between the DBTIMEZONE (+00:00) and the session time zone (-5:00) is 5 hours. Since SYSDATE shows the time as 11:00:00 in the system time zone, the LOCALTIMESTAMP adjusted to the session time zone would show the time as 06:00:00.

The correct answer is A: 11-JUL-2019 6:00:00.00000000 AM – 05:00. This represents the local timestamp in the session time zone, which is 5 hours behind the DBTIMEZONE.

Please note that the exact format returned by LOCALTIMESTAMP includes the fractional seconds up to 9 decimal places, and the time zone offset is specified as part of the timestamp.

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.

A. True. The GROUP BY clause needs to include all non-aggregated columns from the SELECT list to provide the correct grouping for the output. The output shown in the image indicates that the data is grouped by channel_type, month, and country_code.

B, C, and D are incorrect because:

• B includes a ROLLUP which would introduce subtotals that are not reflected in the output shown.
• C specifies a CUBE, which would produce all possible combinations of groupings including the grand total, which is not shown in the output.
• D specifies a ROLLUP on country_code only, which would not correctly group by channel_type and month.

• A. Only the second statement will display departments with no employees. This is true because the second statement uses a LEFT JOIN to include all departments from the departments table, even those without matching entries in the employees table. When there are no employees in a department, the AVG(salary) will be NULL, and the department will still be displayed1.
• C. Both statements will execute successfully if you add e.avg_sal to the select list. This is correct. Both statements calculate e.avg_sal as an average salary, either through a subquery or a join operation. Adding e.avg_sal to the select list will display the average salary alongside the departments. However, it’s important to note that the first statement will not display departments with no employees because it does not use a join that would allow for NULL values from the employees table2.

References:

• Understanding SQL JOINs - Stack Overflow1.
• Oracle Documentation on JOIN Operations2.

Note: The other options are incorrect because:

• B. The first statement will not display departments with no employees since it does not use a join that includes departments without matching employee records.
• D. As explained, the first statement will not display departments with no employees.
• E. There is a typo in the option; it should be E.AVG_SAL. Even if corrected, the first statement alone would not execute successfully because it does not include a join to bring in the avg_sal value.
• F. The second statement will display departments with no employees, but the first statement will not, so this option is incorrect.