database - Need to join double precision foreign key with integer primary key -

what highest performing query joins double precision foreign key integer primary key. tables data vendor, , i'd rather not convert column data type.

in example, fk double precision , pk integer.

should use round?

select this_table.pk, other_table.some_col this_table inner join other_table on other_table.pk = round(this_table.fk)  

or maybe no conversion needed?

thanks.

you can join integers , doubles directly. mysql manage type casting itself. round(double) returns double anyway, not integer.

the joins succeed doubles represent integer. means can directly join 6.0 6; can't directly join 6.000001 6.

if want join 6.000001 6, cast double integer join values in range 6.0 <= 6 < 7.0 . . .

select ... table_with_integers n inner join table_with_doubles d    on cast(d.double_column unsigned integer) = n.integer_column ... 

or use round() join values in range 6.0 <= 6 < 6.5.

the type cast makes more sense if doubles supposed represent integers. if doubles supposed represent integers, shouldn't getting values 6.000001 in first place.