MySQL INSERT with two different UNIQUE constraints -

i have table created with:

create table usersessions (   id integer not null auto_increment,   userid varchar(50) not null,   starttime timestamp null,   endtime timestamp null,   primary key (id),   index(starttime),   index(endtime),   unique(userid, starttime),   unique(userid, endtime) ); 

and want know, if inserting row has duplicate key, on constraint duplicate, on starttime or on endtime. know how it?

name constraints:

create table usersessions (   id integer not null auto_increment,   userid varchar(50) not null,   starttime timestamp null,   endtime timestamp null,   primary key (id),   index(starttime),   index(endtime),   unique idxstarttime(userid, starttime),   unique idxendtime(userid, endtime) ); 

when insert fails error state constraint violated:

#1062 - duplicate entry 'value' key 'idxstarttime'