In the following query, the CASE expression returns a VARCHAR result because the THEN and ELSE clause contains FLOAT and VARCHAR values. The length of the result is 30 since the default format for FLOAT is a string less than 30 characters, and USER is defined as VARCHAR(30) CHARACTER SET UNICODE. The result is CHARACTER SET UNICODE because USER is UNICODE.
SELECT a, CASE WHEN a=1 THEN TIME ELSE USER END FROM table_1 ORDER BY 1;