MDEV-6480: Remove conditions for which range optimizer returned SEL_ARG::IMPOSSIBLE

Let range optimizer remove parts of OR-clauses for which range analysis
produced SEL_TREE(IMPOSSIBLE).
There is no need to remove parts of AND-clauses: either they are inside
of OR (and the whole AND-clause will be removed), or the AND-clause is
at the top level, in which case the whole WHERE (or ON) is always FALSE
and this is a degenerate case which receives special treatment.

The removal process takes care not to produce 1-way ORs (in that case
we substitute the OR for its remaining member).

1 files changed, 45 insertions, 0 deletions

diff --git a/mysql-test/r/range_mrr_icp.result b/mysql-test/r/range_mrr_icp.result
index 16b35448c50..62bea71173c 100644
--- a/mysql-test/r/range_mrr_icp.result
+++ b/mysql-test/r/range_mrr_icp.result
@@ -2198,4 +2198,49 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t3	const	PRIMARY	PRIMARY	4	const	1	
 1	SIMPLE	t2	range	a	a	5	NULL	1	Using where; Using index
 drop table t1,t2,t3;
+#
+# MDEV-6480: Remove conditions for which range optimizer returned SEL_ARG::IMPOSSIBLE.
+#
+create table t1(a int);
+insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+create table t2 (a int, b int, c int, key(a), key(b));
+insert into t2
+select 
+A.a + B.a* 10 + C.a * 100,
+A.a + B.a* 10 + C.a * 100,
+12345
+from 
+t1 A, t1 B, t1 C;
+# EXPLAIN EXTENDED should show that 'b > 25 and b < 15' is removed from the WHERE:
+explain extended select * from t2 where (b > 25 and b < 15) or a<44;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t2	range	a,b	a	5	NULL	43	100.00	Using index condition; Rowid-ordered scan
+Warnings:
+Note	1003	select `test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b`,`test`.`t2`.`c` AS `c` from `test`.`t2` where (`test`.`t2`.`a` < 44)
+# EXPLAIN EXTENDED should show that 'b > 25 and b < 15' is removed from the WHERE:
+explain extended select * from t2 where a < 44 or (b > 25 and b < 15);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t2	range	a,b	a	5	NULL	43	100.00	Using index condition; Rowid-ordered scan
+Warnings:
+Note	1003	select `test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b`,`test`.`t2`.`c` AS `c` from `test`.`t2` where (`test`.`t2`.`a` < 44)
+# Here, conditions b will not be removed, because "c<44" is not sargable
+#   and hence (b.. and .. b) part is not analyzed at all:
+explain extended select * from t2 where c < 44 or (b > 25 and b < 15);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t2	ALL	b	NULL	NULL	NULL	1000	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b`,`test`.`t2`.`c` AS `c` from `test`.`t2` where ((`test`.`t2`.`c` < 44) or ((`test`.`t2`.`b` > 25) and (`test`.`t2`.`b` < 15)))
+# EXPLAIN EXTENDED should show that 'b > 25 and b < 15' is removed from the WHERE:
+explain extended select * from t2 where (b > 25 and b < 15) or c < 44;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t2	ALL	b	NULL	NULL	NULL	1000	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b`,`test`.`t2`.`c` AS `c` from `test`.`t2` where ((`test`.`t2`.`c` < 44))
+# Try a case where both OR parts produce SEL_ARG::IMPOSSIBLE:
+explain extended select * from t2 where (b > 25 and b < 15) or (a>55 and a<44);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+Warnings:
+Note	1003	select `test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b`,`test`.`t2`.`c` AS `c` from `test`.`t2` where 0
+drop table t1,t2;
 set optimizer_switch=@mrr_icp_extra_tmp;