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.