Oracle Updated 1z0-071 Exam Questions and Answers by alisa

The TRUNCATE TABLE command in Oracle SQL is used to quickly delete all rows from a table:

Option A:

It retains the indexes defined on the table. TRUNCATE does not affect the structure of the table, including its indexes.

Option D:

It retains the integrity constraints defined on the table. TRUNCATE does not remove or disable integrity constraints, except for unenforced foreign keys.

Options B, C, E, and F are incorrect because:

Option B: TRUNCATE does not drop triggers; it only removes all rows.

Option C: Flashback Table cannot be used after a TRUNCATE because TRUNCATE is a DDL operation that does not generate undo data for flashback.

Option E: A ROLLBACK cannot be used after a TRUNCATE because TRUNCATE is a DDL command that implicitly commits.

Option F: TRUNCATE may deallocate the space used by the table, depending on the database version and specific options used with the TRUNCATE command.

In Oracle Database 12c, the SYSDATE function returns a date value in the current session's date format. The SUBSTR function is used to extract a substring from a string. However, SYSDATE is a DATE data type and not a string, so you cannot directly use SUBSTR on it. Therefore, SYSDATE must first be converted to a character data type using the TO_CHAR function before applying the SUBSTR function.

Therefore, the correct form of the query should be:

SELECT SUBSTR(TO_CHAR(SYSDATE), 1, 5) AS "Result" FROM DUAL;

This converts the current date and time to a string using the default date format and then extracts the first 5 characters from it.

The INTERSECT operator in SQL returns the results that are common to both of the SELECT statements. It functions similarly to a set intersection in mathematics. When comparing rows for the INTERSECT operation, Oracle Database uses all the expressions in the SELECT lists to derive the result set. NULL values are considered equal for the INTERSECT operator.

Evaluating the provided data from the ORDERS and INVOICES tables, let's see which rows have the same ORDER_ID and ORDER_DATE in both tables:

A: Order ID 3 has a NULL order date in the ORDERS table and does not match with any row in the INVOICES table, so it will not be returned.

B: Order ID 2 has a NULL order date in the ORDERS table but has a non-NULL order date in the INVOICES table, so it will not be returned.

C: Order ID 1 has a NULL order date in both tables, but INTERSECT considers NULLs as equal, so this will be returned.

D: Order ID 5 has a date of 01-MAR-2019 in the ORDERS table and 01-APR-2019 in the INVOICES table, so it will not be returned since the dates do not match.

E: Order ID 4 has a date of 01-FEB-2019 in both tables, so this row will be returned as it matches in both.

F: Order ID 3 has a NULL order date in the ORDERS table but has 01-JAN-2019 in the INVOICES table, so it will not be returned.

Based on this analysis, the query will return:

Order ID 1 with a NULL order date.

Order ID 4 with an order date of 01-FEB-2019.

So the correct answer is:

C: True. A UNIQUE constraint in Oracle SQL allows for the inclusion of NULL values; specifically, it permits multiple NULLs in a column or set of columns but ensures that all non-NULL values are unique.

D: True. A PRIMARY KEY constraint can indeed be added to a table after it has been created and even after it has been populated, as long as the existing data does not violate the primary key constraint rules (i.e., all values must be unique and not NULL).

F: True. A UNIQUE constraint can utilize a pre-existing index on the columns it covers. If a suitable index already exists, Oracle can use this index to enforce the constraint, optimizing performance and resource utilization.

G: True. Columns that are part of a FOREIGN KEY constraint can contain NULL values. This is permissible under SQL standards and Oracle implementation, as a NULL foreign key value is considered to not refer to any row in the referenced table and thus does not violate referential integrity.