LP:731124 - Loss of precision on DISTINCT in 5.1-micro

DISTINCT causes loss of precision - the values returned are missing the sub-second part and are grouped together by the second.

This is alspo repeatable in mysql-5.1, but I think it should be fixed regardless so that increased precision is properly handled in all situations.

Test case:

CREATE TABLE t1 (f1 INTEGER);
INSERT INTO t1 VALUES (1),(2),(3);
SELECT DISTINCT TIME( TIMESTAMPADD( MICROSECOND , f1 , '10:10:10' ) ) FROM t1 ;

SELECT TIME( TIMESTAMPADD( MICROSECOND , f1 , '10:10:10' ) ) FROM t1 ;