Oracle PL 1z0-071 Reddit Questions

When using the GROUP BY clause, every column in the SELECT clause that is not an aggregate function must be included in the GROUP BY clause:

A. SELECT dept_id, join_date, SUM(salary) FROM employees GROUP BY dept_id, join_date: This is a valid query because all non-aggregate columns in the SELECT list (dept_id and join_date) are included in the GROUP BY clause.

Queries B and C are invalid because they attempt to nest aggregate functions, which is not allowed. Query D is invalid because join_date is not included in the GROUP BY clause.

References:

Oracle Database SQL Language Reference 12c, specifically the section on GROUP BY clause constraints.

B. True. CURRENT_TIMESTAMP returns the current date and time in the session time zone, which is determined by the SESSIONTIMEZONE setting.

E. True. CURRENT_TIMESTAMP returns a value of the data type TIMESTAMP WITH TIME ZONE.

A and D are incorrect because CURRENT_TIMESTAMP reflects the session time zone, not DBTIMEZONE. C is incorrect because CURRENT_DATE returns the current date with no time component, whereas CURRENT_TIMESTAMP includes both date and time. F is incorrect because SYSTIMESTAMP returns the current date and time from the system clock in the time zone of the database server, which can differ from the session's time zone affecting CURRENT_TIMESTAMP.

A: Insert statements can be done through a view only if all NOT NULL constraints without default values of the base table are included in the view. Therefore, statement A is incorrect.

B: The WITH CHECK OPTION ensures that all DML operations performed through the view result in data that conforms to the view’s defining query. It affects DELETE as well as other DML operations, making statement B incorrect.

C: Similar to inserts, DELETE operations can be done through a view unless the view contains constructs that inherently do not support it, such as certain joins or set operations. Statement C is generally incorrect.

D: If a view does not include all NOT NULL columns without defaults of the underlying table, it cannot be used to add rows because the missing columns will lack values. This makes statement D correct.

E: This statement is incorrect as primary keys do not affect querying through views; they affect insert and update operations where uniqueness and non-nullability are enforced.

F: If the defining query of a view includes DISTINCT, the view generally cannot be used to perform update or insert operations as it may not be able to uniquely determine rows. This makes statement F correct.

This SQL query checks for product IDs (prod_id) from the costs table where the promotion ID (promo_id) is associated with promotions whose costs are less than the maximum promotional cost of all promotions, grouped by the duration of each promotion (calculated as promo_end_date - promo_begin_date). The query is correctly written to fulfill these conditions.

The subquery SELECT MAX(promo_cost) FROM promotions GROUP BY (promo_end_date - promo_begin_date) computes the maximum cost of promotions grouped by their duration, returning the highest cost for each distinct promotion length.

The WHERE promo_cost < ALL (...) clause then filters out the promotions where the promo_cost is less than all of the maximum costs returned by the subquery, ensuring that only promo_ids associated with costs less than the highest cost for any promotion length are considered.

Since this logical structure correctly implements the given requirement, the statement executes successfully and yields the correct results.