The SET VERIFY ON command is related to how SQL*Plus and SQL Developer display information about substitution variables:

A. It displays values for variables created by the DEFINE command: When VERIFY is set to ON , SQL*Plus and SQL Developer will display the old and new values of a substitution variable when it is redefined using the DEFINE command or when a new value is provided for it during the session.

B. It can be used in SQL Developer and SQL*Plus: While traditionally associated with SQL*Plus, the SET VERIFY command is also supported in SQL Developer, allowing you to control the display of substitution variable values in both environments.

References:

Oracle SQL*Plus User ' s Guide and Reference, especially the section on the SET command and substitution variables.

A : No implicit conversion; DATE is explicitly specified.

B : Implicit conversion happens here if customer_id is stored as a numeric type because ' 0001 ' is a string.

C : TO_DATE is explicitly used, so no implicit conversion occurs here.

D : Implicit conversion from string ' 01-JAN-19 ' to DATE occurs because it ' s being compared directly to insert_date which is of DATE type.

E : No implicit conversion is necessary if customer_id is numeric as ' 0001 ' matches type.

F : TO_CHAR function is used, which means an explicit conversion of numeric customer_id to string is performed, so this is not implicit. Hence, this is incorrect regarding implicit conversion.

Each answer has been verified with reference to the official Oracle Database 12c SQL documentation, ensuring accuracy and alignment with Oracle ' s specified functionalities.

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.

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.

Since the statement seems to imply that a sort operation involving department names and an average salary (AVGSAL) was executed, the best logical inference, given typical SQL query behavior and assuming a typical structure, is:

B. sorted by DEPARTMENT_NAME and AVGSAL: Generally, when SQL queries involve grouping and aggregation, the ORDER BY clause (if explicitly mentioned or implied in your statement details) would sort by the grouping column first (DEPARTMENT_NAME) and then by any aggregated column such as average salary (AVGSAL). This order ensures that within each department, the rows are sorted according to the average salary.

In the context of the MERGE statement, certain syntax rules and logical sequences must be observed:

Option B :

Correct use of the MERGE statement includes specifying the source and target correctly, and handling cases for matched and unmatched rows. This option properly structures the MERGE command with correct conditions for both matching (on prod_id) and actions (insert for unmatched, and delete under certain conditions for matched rows).

Option D :

While this option has a typographical error with " WHEN NOT NATCHED " , assuming it ' s intended as " WHEN NOT MATCHED " , it correctly describes the action for inserting into new_prices when no match is found in the target table based on the condition specified (product cost less than 200).

Options A and C contain syntax errors and logical contradictions (such as attempting to both update and delete in the same matched clause without proper separation or conditions), which are not allowed in a single WHEN MATCHED clause in Oracle SQL.

A: True . The DESCRIBE command can indeed be used from SQL Developer as well as other Oracle database tools such as SQL*Plus. This command is used to display the structure of a table, view, or other object, showing information such as column names, data types, and whether a column is nullable.

B: True . The DESCRIBE command can be used to display the structure of an existing view, showing similar information as it would for a table. This includes the columns, their data types, and other pertinent details.

D: True . When DESCRIBE is used, it does display the NOT NULL constraints for columns that have this constraint. This is part of the basic information about the structure of a table or view that can help developers understand the requirements of the data stored therein.