Allow to use index when GROUP BY on field which has DESCENDING index [CORE4529]

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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

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Modified by: @pavel-zotov

priority: Major [ 3 ] => Minor [ 4 ]

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Commented by: Nico Bendlin (nicode)

Adding ORDER BY x DESC results in: PLAN (T ORDER T_X_DESC)

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Modified by: @dyemanov

assignee: Dmitry Yemanov [ dimitr ]

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Modified by: @dyemanov

status: Open [ 1 ] => Resolved [ 5 ]

resolution: Fixed [ 1 ]

Fix Version: 4.0 Beta 1 [ 10750 ]

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Modified by: @dyemanov

Component: Engine [ 10000 ]

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Modified by: @pavel-zotov

status: Resolved [ 5 ] => Resolved [ 5 ]

QA Status: Done successfully

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Modified by: @pavel-zotov

status: Resolved [ 5 ] => Closed [ 6 ]