Bug#16712: group_concat returns odd srting insead of intended result

  when calculating GROUP_CONCAT all blob fields are transformed
  to varchar when making the temp table.
  However a varchar has at max 2 bytes for length. 
  This fix makes the conversion only for blobs whose max length 
  is below that limit. 
  Otherwise blob field is created by make_string_field() call.


mysql-test/r/func_gconcat.result:
  Bug#16712: group_concat returns odd srting insead of intended result
    * testsuite for the bug
mysql-test/t/func_gconcat.test:
  Bug#16712: group_concat returns odd srting insead of intended result
    * testsuite for the bug
sql/item_sum.cc:
  Bug#16712: group_concat returns odd srting insead of intended result
    * force blob->varchar conversion for small enough blobs only
sql/sql_select.cc:
  Bug#16712: group_concat returns odd srting insead of intended result
    * force blob->varchar conversion for small enough blobs only

1 files changed, 14 insertions, 0 deletions

diff --git a/mysql-test/t/func_gconcat.test b/mysql-test/t/func_gconcat.test
index fbfdfa3b5d0..98c21986aa9 100644
--- a/mysql-test/t/func_gconcat.test
+++ b/mysql-test/t/func_gconcat.test
@@ -433,3 +433,17 @@ create table t1 (c1 varchar(10), c2 int);
 select charset(group_concat(c1 order by c2)) from t1;
 drop table t1;
 
+#
+# Bug #16712: group_concat returns odd string instead of intended result
+#
+CREATE TABLE t1 (a INT(10), b LONGTEXT, PRIMARY KEY (a));
+
+SET GROUP_CONCAT_MAX_LEN = 20000000;
+
+INSERT INTO t1 VALUES (1,REPEAT(CONCAT('A',CAST(CHAR(0) AS BINARY),'B'), 40000));
+INSERT INTO t1 SELECT a + 1, b FROM t1;
+
+SELECT a, CHAR_LENGTH(b) FROM t1;
+SELECT CHAR_LENGTH( GROUP_CONCAT(b) ) FROM t1;
+SET GROUP_CONCAT_MAX_LEN = 1024;
+DROP TABLE t1;