Fix for bug #32202: ORDER BY not working with GROUP BY

The bug is a regression introduced by the fix for bug30596. The problem
was that in cases when groups in GROUP BY correspond to only one row,
and there is ORDER BY, the GROUP BY was removed and the ORDER BY
rewritten to ORDER BY <group_by_columns> without checking if the
columns in GROUP BY and ORDER BY are compatible. This led to
incorrect ordering of the result set as it was sorted using the
GROUP BY columns. Additionaly, the code discarded ASC/DESC modifiers
from ORDER BY even if its columns were compatible with the GROUP BY
ones.

This patch fixes the regression by checking if ORDER BY columns form a
prefix of the GROUP BY ones, and rewriting ORDER BY only in that case,
preserving the ASC/DESC modifiers. That check is sufficient, since the
GROUP BY columns contain a unique index.


mysql-test/r/group_by.result:
  Added a test case for bug #32202.
mysql-test/t/group_by.test:
  Added a test case for bug #32202.
sql/sql_select.cc:
  In cases when groups in GROUP BY correspond to only one row and there
  is ORDER BY, rewrite the query to ORDER BY <group_by_columns> only if
  the columns in ORDER BY and GROUP BY are compatible, i.e. either one
  forms a prefix for another.

1 files changed, 35 insertions, 0 deletions

diff --git a/mysql-test/t/group_by.test b/mysql-test/t/group_by.test
index b7c28cada46..b150db6dafe 100644
--- a/mysql-test/t/group_by.test
+++ b/mysql-test/t/group_by.test
@@ -815,3 +815,38 @@ EXPLAIN SELECT c,b   FROM t1 GROUP BY c,b;
 SELECT c,b   FROM t1 GROUP BY c,b;
 
 DROP TABLE t1;
+
+#
+# Bug #32202: ORDER BY not working with GROUP BY
+#
+
+CREATE TABLE t1(
+  id INT AUTO_INCREMENT PRIMARY KEY, 
+  c1 INT NOT NULL, 
+  c2 INT NOT NULL,
+  UNIQUE KEY (c2,c1));
+
+INSERT INTO t1(c1,c2) VALUES (5,1), (4,1), (3,5), (2,3), (1,3);
+
+# Show that the test cases from the bug report pass
+SELECT * FROM t1 ORDER BY c1;
+SELECT * FROM t1 GROUP BY id ORDER BY c1;
+
+# Show that DESC is handled correctly
+SELECT * FROM t1 GROUP BY id ORDER BY id DESC;
+
+# Show that results are correctly ordered when ORDER BY fields
+# are a subset of GROUP BY ones
+SELECT * FROM t1 GROUP BY c2 ,c1, id ORDER BY c2, c1;
+SELECT * FROM t1 GROUP BY c2, c1, id ORDER BY c2 DESC, c1;
+SELECT * FROM t1 GROUP BY c2, c1, id ORDER BY c2 DESC, c1 DESC;
+
+# Show that results are correctly ordered when GROUP BY fields
+# are a subset of ORDER BY ones
+SELECT * FROM t1 GROUP BY c2  ORDER BY c2, c1;
+SELECT * FROM t1 GROUP BY c2  ORDER BY c2 DESC, c1;
+SELECT * FROM t1 GROUP BY c2  ORDER BY c2 DESC, c1 DESC;
+
+DROP TABLE t1;
+
+--echo End of 5.0 tests