The SQL UNION operator is designed to combine the result sets of two or more SELECT statements into a single result set. A key characteristic of the UNION operator is that it automatically removes duplicate rows from the final result. The analyst's task is to merge records from the "Employees" and "Managers" tables and eliminate any duplicates between them. The statement SELECT FROM Employees UNION SELECT FROM Managers correctly performs this operation by vertically appending the two tables and filtering out any identical rows, thus achieving the desired outcome.

A. UNION ALL combines result sets but includes all rows, including duplicates, which fails to meet the requirement to remove them.

C. The JOIN syntax is invalid, and its purpose is to combine columns from different tables based on a related key, not to combine rows.

D. CROSS JOIN creates a Cartesian product, pairing every row from the first table with every row from the second, which is not the required operation.

1. PostgreSQL 16 Documentation. (n.d.). 7.4. Combining Queries. PostgreSQL. Retrieved from https://www.postgresql.org/docs/16/queries-union.html. In Section 7.4

the documentation states

"The UNION operator computes the set union of the rows returned by the involved SELECT statements. A row is in the set union of two result sets if it appears in at least one of the result sets. ... Duplicate rows are eliminated from the result..."

2. Oracle Database SQL Language Reference

23c. (n.d.). Set Operators. Oracle. Retrieved from https://docs.oracle.com/en/database/oracle/oracle-database/23/sqlrf/Set-Operators.html#GUID-B0F24731-B6B5-465F-940E-25D617553A0E. The documentation specifies

"The UNION operator returns the distinct rows from the result sets of the two queries." It contrasts this with UNION ALL

which "does not eliminate duplicate rows."

3. Ullman

J. D.

& Widom

J. (n.d.). CS145 Introduction to Databases

Lecture Notes: SQL 2. Stanford University. Retrieved from https://web.stanford.edu/class/cs145/notes/SQL-2.pdf. On page 2

under "Union

Intersection

Difference

" the notes explain that (SELECT ... FROM ... WHERE ...) UNION (SELECT ... FROM ... WHERE ...) computes the set union and that "UNION removes duplicates."