Concatenation Showplan Operator
The Concatenation operator scans multiple inputs, returning each row scanned. Concatenation is typically used to implement the Transact-SQL UNION ALL construct.
The Concatenation physical operator has two or more inputs and one output. Concatenation copies rows from the first input stream to the output stream, then repeats this operation for each additional input stream.
Concatenation is a logical and physical operator.
.gif "Concatenation operator icon")
Graphical execution plan icon