CHOOSE function returns the data type with the highest precedence from the set of types passed to the function.
Example,
SELECT CHOOSE(4, 1, 'Option1', GETDATE(), 3.14159, PI() ) AS [FourthValueAsOutput]
Output:
FourthValueAsOutput
1900-01-04 03:23:53.373
Here, the fourth value in the list is
3.14159 ; but the result is a DATETIME value.
The highest precedence from list of above values in the CHOOSE is DATETIME' So the result 3.14159 is added to default datetime value '1900-01-01'