MySQL Filters part of field duplicate data

Select distinct can remove duplicate records.

Disctinct ignores duplicate records, but it ignores identical duplicate records, not records that are duplicated in one of these fields, or where a distinct queries a field so that multiple fields are not.

So using aggregate functions and GROUP by implementations

Note: Group by can only be used with aggregate functions

Example table

ID username Password Trdesc ........ ......... ...

1 A abcdef QR

2 A abcdef W34

3 A bbbbbb AD

4 B aaaaaa ASDF

Query username and password combination of conditions can not be repeated query results (this can be repeated, not to mention that this is a mess)

When username and password Repeat, take the record with the largest ID:

SELECT * FROM MyTable where ID in (select Max (ID) from MyTable Group by Username,password)

When username and password Repeat, take the record with the lowest ID:

SELECT * FROM MyTable where ID in (select min (ID) from MyTable a group by Username,password)