1z0-071 Exam Dumps - Oracle PL Questions and Answers

E. True. Indexes can be created on global temporary tables just like they can on permanent tables. The indexes on global temporary tables are also temporary and only exist for the duration of the session or transaction, based on how the table was defined.

F. True. If the ON COMMIT clause is specified as DELETE ROWS, then all rows in the global temporary table are deleted after each COMMIT or ROLLBACK within the transaction. This clause defines the scope of the data's persistence within the global temporary table.

C. True, when performing a self join, aliases are used to differentiate the same table in different contexts within the same query. This helps in comparing different rows within the same table as if they were in two separate tables.D. True, the ON clause can be used in self joins to specify the conditions on which the join is based. This is a standard method for specifying join conditions in SQL.F. True, a self join can be an outer join, allowing for the inclusion of rows that do not have a matching row in the same table according to the join condition. This enhances the flexibility of data analysis and reporting.

References:

Oracle documentation on joins: Oracle Database SQL Language Reference

Details on self joins and outer joins: Oracle Joins Tutorial

The data dictionary contains metadata (data about data) about the database and its objects.

A. False. DBA_ views display metadata for objects accessible to the database administrator, not only for the SYS schema.

B. True. ALL_ views display information about all the objects that the current user has access to. This does not necessarily mean the user has privileges on these objects, only that the user can see them.

C. False. The data dictionary is not accessible when the database is closed because it requires the database to be open in order to access the system tables.

D. True. Not all types of metadata are available in all three prefixes (ALL_, DBA_, USER_). Some specific metadata might only be available in one or two of these view types.

E. False. The data dictionary stores metadata in tables. The various views (ALL_, DBA_, USER_, etc.) provide different perspectives on this data.

References:

Oracle Documentation on Data Dictionary and Dynamic Performance Views: https://docs.oracle.com/cd/B28359_01/server.111/b28310/datadict.htm

INVISIBLE indexes are a feature in Oracle Database 12c and later versions that allow an index to be maintained but not used by the optimizer unless explicitly hinted.

A. False. An INVISIBLE index still consumes storage space as it is maintained in the background.

B. False. There is no such restriction. You can create multiple INVISIBLE indexes on the same column list.

C. False. The optimizer can consider INVISIBLE indexes if they are hinted at in the query.

D. True. You can alter the visibility of an index using the ALTER INDEX command to make an INVISIBLE index VISIBLE.

E. True. Even though they are invisible to the optimizer by default, all DML operations such as INSERT, UPDATE, and DELETE continue to maintain the index as they would with a VISIBLE index.

Single-row functions in SQL operate on each row independently and can modify the returned value:

Option A: Incorrect. Single row functions can be used in multiple parts of a SELECT statement, including SELECT, WHERE, and ORDER BY clauses.

Option B: Incorrect. Single row functions can accept more than one argument, such as the CONCAT function, which can accept multiple string arguments.

Option C: Incorrect. They return one result for each row processed, not per table.

Option D: Correct. Single row functions can take various types of arguments including column names, literals, variables, and other expressions.

Option E: Correct. Functions can be nested within other functions, allowing complex expressions and calculations.

Option F: Correct. The data type of the result can differ from the arguments’ data types, such as the SUBSTR function returning a VARCHAR2 even when used on a number after converting it to a string.

A. True - The TO_CHAR function is used correctly here to convert the numeric value to a string, and NVL handles the case where cust_credit_limit might be NULL. The expression inside NVL computes 15% of the credit limit or displays 'Not Available' if the credit limit is NULL. The syntax is correct.

B. False - The NVL2 function requires three parameters: the expression to check for NULL, the value to return if it's not NULL, and the value to return if it is NULL. The given usage lacks the required parameters and syntax.

C. False - The NVL function expects both parameters to be of the same data type. Since the second parameter 'Not Available' is a string, it causes a data type conflict with the numerical result of the first parameter.

D. False - The keyword SELECT is misspelled as SLECT, making the syntax incorrect.

E. True - This query uses NVL2 correctly by checking if cust_credit_limit is not NULL, then applying TO_CHAR to compute 15% of it and converting it to string, or returning 'NOT Available' if it is NULL. The syntax and function usage are correct.

To find customer names where the last name starts with Mc or MC, the correct queries are:

A. WHERE UPPER(SUBSTR(cust_name, INSTR(cust_name, ' ') + 1)) LIKE 'MC%'This query converts the substring of cust_name that comes after the first space (which should correspond to the last name) to uppercase and checks if it starts with 'MC', which will match both 'Mc' and 'MC'.

E. WHERE SUBSTR(cust_name, INSTR(cust_name, ' ') + 1) LIKE 'Mc%'This query checks if the substring of cust_name after the first space starts with 'Mc'. However, this query will only match last names that start with 'Mc' and not 'MC' unless the database is using a case-insensitive collation.

Options B, C, and D are incorrect:

B is incorrect because the syntax is not valid in Oracle SQL; the LIKE clause cannot be used to match multiple patterns in that way.

C is incorrect because INITCAP would not only capitalize the first letter of 'mc' or 'Mc' but would lowercase all other letters, which is not the intended action.

D is incorrect because, like option C, INITCAP is not the appropriate function for this use case and it will not correctly identify names that start with 'MC'.

A. This statement is incorrect. An INVISIBLE index is maintained during DML operations just like a VISIBLE index. The difference is that an INVISIBLE index is not used by the optimizer unless explicitly hinted. B. This statement is correct. When creating a table, you can define indexes on one or more columns as part of the table definition. C. This statement is incorrect. While a DROP INDEX statement will drop the index, it does not always prevent updates to the table. If the index is marked as unusable or is an invisible index, for example, updates can still be performed. D. This statement is correct. It is possible to have both a UNIQUE index and a non-unique index on the same column. The UNIQUE index enforces the uniqueness of column values, while the non-unique index does not. E. This statement is correct to some extent. Descending indexes are not function-based indexes per se, but they are indexes on which the data is sorted in descending order, as opposed to the default ascending order. However, descending indexes are conceptually related to function-based indexes because they alter the way the indexed data is stored. F. This statement is incorrect. The use of an index in query execution depends on the optimizer's decision, which is based on statistics and the cost associated with using the index. There are situations where the optimizer may choose a full table scan even if there is an index on the filter column.

References can be found in the Oracle Database Concepts Guide and the SQL Language Reference documentation, which detail the behavior of indexes and how they are managed within the Oracle database.

D: True. This query selects the first name and calculates the due amount as 5% of the credit limit from the customers table where the income level is not null and the credit limit is also not null. The IS NOT NULL operator is used to check for non-null values correctly.

The IS NOT NULL operator is the correct way to check for non-null values in SQL. The <> NULL and != NULL comparisons are incorrect because NULL is not a value that can be compared using these operators; it represents the absence of a value.

There is no due_amount column in the customers table according to the structure provided, so any WHERE clause referencing due_amount is irrelevant and incorrect. The due_amount is a derived column in the SELECT clause.

The correct syntax to check for non-null values is IS NOT NULL, which is used in the WHERE clause of the correct answer.

References:

The use of IS NOT NULL in the WHERE clause to filter out null values is documented in Oracle's SQL reference.

NULL comparisons must be done with IS NULL or IS NOT NULL for correct logical evaluation in SQL.

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.