What is the reason for not being able to retrieve table names with a UNION query?

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A UNION query combines the results of two or more SELECT statements into a single result set. When using UNION, the column names and data types of the result set are determined by the column names and data types of the first SELECT statement. Therefore, the names of the tables used in subsequent SELECT statements are not needed or recorded. As a result, it is not possible to retrieve table names with a UNION query.