Fix cost calculation for get_best_group_min_max()

If the final range restrictions (SEL_ARG tree) over GROUP BY
columns are single-point, we can compute the number of GROUP BY groups.

Example: in the query:
SELECT ... FROM tbl
WHERE keypart1 IN (1,2,3) and keypart2 IN ('foo','bar')

Other things:
- Fixed cost calculation to more correctly count the number of blocks
  that may be read. The old code could use the total blocks in the file
  even if a range was available.

1 files changed, 23 insertions, 1 deletions

diff --git a/mysql-test/main/group_by.test b/mysql-test/main/group_by.test
index 87f82fde5ce..3aa7f1cd0d3 100644
--- a/mysql-test/main/group_by.test
+++ b/mysql-test/main/group_by.test
@@ -718,7 +718,8 @@ drop table t1, t2;
 CREATE TABLE t1 (a tinyint(3), b varchar(255), PRIMARY KEY  (a));
 
 INSERT INTO t1 VALUES (1,'-----'), (6,'Allemagne'), (17,'Autriche'), 
-    (25,'Belgique'), (54,'Danemark'), (62,'Espagne'), (68,'France');
+    (25,'Belgique'), (54,'Danemark'), (62,'Espagne'), (68,'France'),
+    (100,"No land"), (101,"No land");
 
 CREATE TABLE t2 (a tinyint(3), b tinyint(3), PRIMARY KEY  (a), KEY b (b));
 
@@ -1168,7 +1169,9 @@ SELECT b from t2 GROUP BY b;
 
 # Show that we are using 'range' when there is more NULL rows in the table
 insert into t2 SELECT NULL, NULL from seq_1_to_10;
+EXPLAIN SELECT b from t2 GROUP BY a;
 --echo # Expect: Using index for group-by
+analyze table t2;
 EXPLAIN SELECT b from t2 GROUP BY a;
 
 DROP TABLE t1;
@@ -2131,3 +2134,22 @@ drop table t20, t21, t22;
 --echo #
 --echo # End of 10.3 tests
 --echo #
+
+--echo #
+--echo # Test new group_min_max optimization
+--echo #
+
+create table t1 (a int, b int, c int, key(a,b,c));
+insert into t1 select mod(seq,23),mod(seq,13), mod(seq,5) from seq_1_to_10000;
+
+explain select a from t1 where a in (1,2,3) group by a;
+explain select a from t1 where a in (1,2,3) or a = 22 group by a;
+explain select a from t1 where a in (1,2,3) and a < 3 group by a;
+explain select a,b from t1 where (a) in (1,2,3) and b in (5,6,7) group by a,b;
+explain select a,b from t1 where (a,b) in ((1,1),(2,2),(3,3)) group by a,b;
+explain select a,b,c from t1 where (a,b) in ((1,1),(2,2),(3,3)) and c=3 group by a,b,c;
+
+--echo # Will not use index for group-by
+explain select a from t1 where a in (1,2,3) and b>1 group by a;
+explain select a from t1 where a in (1,2,3) and c=1 group by a;
+drop table t1;