Pass the Oracle Oracle PL 1z0-071 Questions and answers with CertsForce

When performing DML operations on a view, certain restrictions apply:

D. Views cannot be used to add or modify rows in an underlying table if the defining query of the view contains the DISTINCT keyword: If the defining query of a view contains the DISTINCT keyword, it cannot be used for certain DML operations, such as INSERT and UPDATE, because the set of rows it represents is not directly modifiable.

E. Views cannot be used to add or modify rows in an underlying table if the defining query of the view contains aggregating functions: Aggregating functions create a result that summarises multiple rows and cannot be reversed to point to a single row for modification.

F. Views cannot be used to add rows to an underlying table if the table has columns with NOT NULL constraints lacking default values which are not referenced in the defining query of the view: If a column with a NOT NULL constraint is not included in the view's defining query, and it does not have a default value, it is not possible to insert through the view because it would violate the NOT NULL constraint.

References:

Oracle Database SQL Language Reference 12c, particularly the sections on views and the restrictions on DML operations through views.

Regarding INTERVAL data types in Oracle Database 12c:

A. INTERVAL YEAR TO MONTH columns only support monthly intervals within a range of years. This is true. The INTERVAL YEAR TO MONTH data type stores a period of time using years and months.

E. INTERVAL DAY TO SECOND columns support fractions of seconds. This is true. The INTERVAL DAY TO SECOND data type can store days, hours, minutes, seconds, and fractional seconds.

Options B, C, D, and F are incorrect:

B is incorrect because data types between INTERVAL DAY TO SECOND and INTERVAL YEAR TO MONTH are not compatible.

C is incorrect as it incorrectly limits INTERVAL YEAR TO MONTH to a single year.

D is incorrect; the YEAR field can be negative to represent a past interval.

F is incorrect as INTERVAL YEAR TO MONTH supports intervals that can span multiple years, not just annual increments.

A. True. When using set operators, the number and order of columns must be the same in all SELECT statements involved in the query. The data types of those columns must also be compatible.

E. True. The FOR UPDATE clause cannot be specified in a subquery or a SELECT statement that is combined with another SELECT statement by using a set operator.

B is incorrect because the column names do not need to match; only the number and data types of the columns must be compatible. C is incorrect because only the final SELECT statement in the sequence of UNION/INTERSECT/MINUS operations can have an ORDER BY clause. D is incorrect because, as of Oracle 12c, UNION ALL can be used with CLOB columns, but UNION, INTERSECT, and MINUS cannot.

When the NLS_DATE_FORMAT is set to DD Mon YYYY, the database expects the date string to be in the format of day, abbreviated month name, and full year.

B. The query SELECT DATE '2019-01-01' FROM DUAL; correctly returns the value 1 Jan 2019 because the ANSI date literal DATE 'YYYY-MM-DD' is independent of the NLS_DATE_FORMAT parameter.

Option A is incorrect because the TO_DATE function requires the format model to match the string literal, which it does not in this case.

Option C is incorrect because TO_CHAR is used to convert a date to a string, not a string to a date.

Option D is incorrect because without specifying that the string is a date, the result is just a string and not a date value.

Option E is incorrect because TO_DATE without a format model relies on the NLS_DATE_FORMAT to interpret the string, and YYYY-MM-DD does not match DD Mon YYYY.

When performing DML operations on a view without INSTEAD OF triggers:

Option C: Views cannot be used to add rows to an underlying table if the table has columns with NOT NULL constraints lacking default values which are not referenced in the defining query of the view.

This is true because the view would not provide values for NOT NULL columns without defaults, leading to an error.

Option D: Views cannot be used to add or modify rows in an underlying table if the defining query of the view contains the DISTINCT keyword.

Using DISTINCT in the view’s defining query can make the view non-updatable, as it may aggregate multiple rows into one.

Option E: Delete statements can always be done on a table through a view.

Deletes through a view are typically unrestricted as long as the view does not involve aggregates, DISTINCT, or similar constructs that would logically preclude determining which underlying rows should be deleted.

In Oracle SQL, the q quote operator can be used to define string literals that contain single quotes or other special characters without needing to escape them. The queries using the q quote mechanism, like in options A and C, will successfully return the string as it is, including single quotes within the string.

A: Correct, it uses the q quote operator with the exclamation mark ! as the delimiter, which allows the string to contain single quotes.

B: Incorrect, double quotes " in Oracle SQL are used for identifiers such as column names, not string literals.

C: Correct, this also uses the q quote operator, with the square brackets [] as the delimiters.

D: Incorrect, the backslash \ is not used as an escape character in Oracle SQL string literals, and the ESCAPE keyword is used incorrectly here.

E: Incorrect, this does not account for the single quote within the string, which would terminate the string literal prematurely, and it lacks the q quote operator or proper escape mechanism.

Data Manipulation Language (DML) operations in Oracle 12c are critical for handling data within tables. Here’s the validity of each statement based on Oracle SQL documentation:

Option A: True. The DELETE statement can remove multiple rows from a table and supports the use of multiple conditions in the WHERE clause to specify which rows should be removed. This allows for flexibility in managing data deletion based on various criteria.

Option B: True. The INSERT statement can explicitly insert NULL values into a column, assuming there are no constraints (like NOT NULL) preventing such entries. This is useful for representing the absence of data or when data is unknown.

Option C: False. DML statements like INSERT INTO...SELECT...FROM do not automatically commit in Oracle. Transactions in Oracle require explicit COMMIT commands to finalize changes, unless in an autocommit mode set by a client tool or environment, which is generally not the default behavior for server-side operations.

Option D: False. DML statements do not require a primary key to be defined on a table. While having a primary key is a best practice for identifying each row uniquely, it's not a prerequisite for performing DML operations like INSERT, UPDATE, or DELETE.

Option E: True. The UPDATE statement can include different subqueries within the SET clause to determine the values for each column being updated. This allows for complex calculations and data retrieval to be part of an update, increasing the power and flexibility of data modification.

Analyzing the given SQL statements on the ORDER_ITEMS table:

D. Statement 2 may return multiple rows of output: Statement 2 groups the results by ORDER_ID, which means it calculates the maximum UNIT_PRICE * QUANTITY for each ORDER_ID, potentially returning multiple rows depending on the number of unique ORDER_IDs in the table.

E. Statement 1 returns only one row of output: Statement 1 computes the maximum product of UNIT_PRICE and QUANTITY across all entries in the ORDER_ITEMS table, returning a single row with the maximum value.

Incorrect options:

A: Since Statement 2 groups by ORDER_ID, it does not necessarily return just one row; it returns one row per ORDER_ID.

B: These statements do not yield the same output; Statement 1 returns a single maximum value, while Statement 2 returns the maximum value per ORDER_ID.

C: If either UNIT_PRICE or QUANTITY is NULL, the product for that row will be NULL, but the MAX function ignores NULL values in its calculation unless all rows are NULL, in which case it returns NULL.

B: True. The MAX and MIN functions can be applied to columns with character data types. These functions will return the highest or lowest values in a set of rows, based on alphabetical order for character data. This allows these aggregate functions to be versatile and useful across different data types, including numerical, date, and character types.

Given the statements, the failure to execute would be due to improper SQL syntax or logical structuring of the JOIN clause:

A. SELECT * FROM employees e JOIN department d WHERE e.department_id=d.department_id AND d.department_id=90: This statement will fail because it incorrectly uses the JOIN syntax without an ON clause, which is necessary to specify the condition on which the tables are joined. This statement mistakenly places the join condition in the WHERE clause without using ON.

Correct options (executes successfully):

B: Correctly formulated JOIN with ON and an additional condition in the WHERE clause.

C: Incorporates the filtering directly in the ON clause, which is a valid method to restrict the rows returned by the JOIN based on conditions related to both tables.

D: Although it appears awkward due to the order of conditions in the ON clause, it is syntactically correct.

These answers reflect typical use and constraints in SQL queries and are aligned with Oracle Database 12c standards for SQL syntax and operations.