Fix bug MDEV-641

Analysis:
Range analysis discoveres that the query can be executed via loose index scan for GROUP BY.
Later, GROUP BY analysis fails to confirm that the GROUP operation can be computed via an
index because there is no logic to handle duplicate field references in the GROUP clause.
As a result the optimizer produces an inconsistent plan. It constructs a temporary table,
but on the other hand the group fields are not set to point there.
    
Solution:
Make loose scan analysis work in sync with order by analysis. In the case of duplicate
columns loose scan will not be applicable. This limitation will be lifted in 10.0 by
removing duplicate columns.

1 files changed, 74 insertions, 0 deletions

diff --git a/mysql-test/t/group_by.test b/mysql-test/t/group_by.test
index 8f38f0e9fd9..d9ec637b012 100644
--- a/mysql-test/t/group_by.test
+++ b/mysql-test/t/group_by.test
@@ -1315,4 +1315,78 @@ SELECT 1 FROM t1 GROUP BY SUBSTRING(SYSDATE() FROM 'K' FOR 'jxW<');
 DROP TABLE t1;
 SET SQL_BIG_TABLES=0;
 
+--echo #
+--echo # MDEV-641 LP:1002108 - Wrong result (or crash) from a query with duplicated field in the group list and a limit clause
+--echo # Bug#11761078: 53534: INCORRECT 'SELECT SQL_BIG_RESULT...' 
+--echo #               WITH GROUP BY ON DUPLICATED FIELDS
+--echo #
+
+CREATE TABLE t1(
+ col1 int, 
+ UNIQUE INDEX idx (col1));
+
+INSERT INTO t1 VALUES (1),(2),(3),(4),(5),(6),(7),(8),(9),(10),
+   (11),(12),(13),(14),(15),(16),(17),(18),(19),(20);
+
+let $query0=SELECT col1 AS field1, col1 AS field2
+            FROM t1 GROUP BY field1, field2;
+
+# Needs to be range to exercise bug
+--eval EXPLAIN $query0;
+FLUSH STATUS;
+--eval $query0;
+SHOW SESSION STATUS LIKE 'Sort_scan%';
+
+let $query=SELECT SQL_BIG_RESULT col1 AS field1, col1 AS field2
+           FROM t1 GROUP BY field1, field2;
+
+# Needs to be range to exercise bug
+--eval EXPLAIN $query;
+FLUSH STATUS;
+--eval $query;
+SHOW SESSION STATUS LIKE 'Sort_scan%';
+
+CREATE VIEW v1 AS SELECT * FROM t1;
+
+SELECT SQL_BIG_RESULT col1 AS field1, col1 AS field2
+FROM v1 
+GROUP BY field1, field2; 
+
+SELECT SQL_BIG_RESULT tbl1.col1 AS field1, tbl2.col1 AS field2
+FROM t1 as tbl1, t1 as tbl2 
+GROUP BY field1, field2 
+LIMIT 3;
+
+explain
+select col1 f1, col1 f2 from t1 order by f2, f1;
+select col1 f1, col1 f2 from t1 order by f2, f1;
+
+explain
+select col1 f1, col1 f2 from t1 group by f2 order by f2, f1;
+select col1 f1, col1 f2 from t1 group by f2 order by f2, f1;
+
+explain
+select col1 f1, col1 f2 from t1 group by f1, f2 order by f2, f1;
+select col1 f1, col1 f2 from t1 group by f1, f2 order by f2, f1;
+
+CREATE TABLE t2(
+ col1 int, 
+ col2 int, 
+ UNIQUE INDEX idx (col1, col2));
+
+INSERT INTO t2(col1, col2) VALUES
+   (1,20),(2,19),(3,18),(4,17),(5,16),(6,15),(7,14),(8,13),(9,12),(10,11),
+   (11,10),(12,9),(13,8),(14,7),(15,6),(16,5),(17,4),(18,3),(19,2),(20,1);
+
+explain
+select col1 f1, col2 f2, col1 f3 from t2 group by f1, f2, f3;
+select col1 f1, col2 f2, col1 f3 from t2 group by f1, f2, f3;
+
+explain
+select col1 f1, col2 f2, col1 f3 from t2 order by f1, f2, f3;
+select col1 f1, col2 f2, col1 f3 from t2 order by f1, f2, f3;
+
+DROP VIEW v1;
+DROP TABLE t1, t2;
+
 --echo # End of 5.1 tests