To determine which MERGE statement is valid, we need to examine the syntax of each option and compare it to the requirements of the question.
The question provides two tables: EMPLOYEES and NEW EMPLOYEES. Both tables have an EMPLOYEE_ID column as the primary key. The goal of the MERGE statement is to update the NAME column in the NEW EMPLOYEES table with the concatenated FIRST_NAME and LAST_NAME values from the EMPLOYEES table. If an employee exists in the NEW EMPLOYEES table, the NAME should be updated. If the employee does not exist, a new row should be inserted.
Now let's examine each option:
A. MERGE INTO new_employees c USING employees e ON (c.employee_id = e.employee_id) WHEN MATCHED THEN UPDATE SET c.name = e.first_name ||','|| e.last_name WHEN NOT MATCHED THEN INSERT VALUES(e.employee_id, e.first_name ||', '||e.last_name);
This option is valid. It uses the correct syntax for a MERGE statement and joins the two tables on the EMPLOYEE_ID column. It updates the NAME column in the NEW EMPLOYEES table with the concatenated FIRST_NAME and LAST_NAME values from the EMPLOYEES table. If a match is not found, a new row is inserted into the NEW EMPLOYEES table.
B. MERGE new_employees c USING employees e ON (c.employee_id = e.employee_id) WHEN EXISTS THEN UPDATE SET c.name = e.first_name ||','|| e.last_name WHEN NOT MATCHED THEN INSERT VALUES(e.employee_id, e.first_name ||', '||e.last_name);
This option is invalid. It uses the correct syntax for a MERGE statement, but the WHEN EXISTS clause is not valid. It should be WHEN MATCHED instead. Additionally, the syntax for the UPDATE clause is incorrect.
C. MERGE INTO new employees c USING employees e ON (c.employee_id = e.employee_id) WHEN EXISTS THEN UPDATE SET c.name = e.first_name ||','|| e.last_name WHEN NOT MATCHES THEN INSERT VALUES(e.employee_id, e.first_name ||', '||e.last_name);
This option is invalid. It has a syntax error in the WHEN NOT MATCHES clause, which should be WHEN NOT MATCHED. Additionally, the UPDATE clause syntax is incorrect.
D. MERGE new_employees c FROM employees e ON (c.employee_id = e.employee_id) WHEN MATCHED THEN UPDATE SET c.name = e.first_name ||','|| e.last_name WHEN NOT MATCHED THEN INSERT INTO new_employees VALUES(e.employee_id, e.first_name ||'.'||e.last_name);
This option is invalid. It does not use the correct syntax for a MERGE statement. Additionally, the INSERT INTO clause syntax is incorrect.
Thus, the valid MERGE statement is:
The Answer is: A. MERGE INTO new_employees c USING employees e ON (c.employee_id = e.employee_id) WHEN MATCHED THEN UPDATE SET c.name = e.first_name ||','|| e.last_name WHEN NOT MATCHED THEN INSERT VALUES(e.employee_id, e.first_name ||', '||e.last_name);