Submitted by: @pavel-zotov

SQL> recreate table t(x int, y int); commit;
SQL> insert into t select rand()*5, rand()*5 from rdb$types, rdb$types; commit;
SQL> create DESCENDING index t_x_desc on t(x); commit;
SQL> set planonly;
SQL> select x,max(y) from t group by x;

PLAN SORT (T NATURAL) -- ? :(

SQL> select x,min(y) from t group by x;

PLAN SORT (T NATURAL) -- ? :(

SQL> set planonly;
SQL> drop index t_x_desc; commit;

---------- compare when ASC index on this field: --------

SQL> create index t_x_asc on t(x); commit;
SQL> set planonly;
SQL> select x,max(y) from t group by x;

PLAN (T ORDER T_X_ASC)
SQL> select x,min(y) from t group by x;

PLAN (T ORDER T_X_ASC)
SQL> set planonly;
SQL> drop index t_x_asc; commit;

PS. LI-T3.0.0.31288

Commits: 40c7b29