[GENERAL] How to select rows that are the max for each subcategory?

Suppose I have a table T that has, among its columns, the fields X and Y, where Y is an integer, and multiple rows with the same value of X are possible.  I want to select the rows corresponding to the greatest values of Y for each value of X.  E.g. suppose that T is

X Y Z

a  1 eenie

a  3 meenie

a  2 miny

b  4 moe

b  0 catch

...the result of the desired query would be

a  3 meenie

b  4 moe

TIA!

Kynnjo