Bug#23451 GROUP_CONCAT truncates a multibyte utf8 character

  
  Problem: GROUP_CONCAT on a multi-byte column can truncate
  in the middle of a multibyte character when applying
  group_concat_max_len limit. It produces an invalid
  multi-byte character in the result string.
  
The second, easier version - reusing old "warning_for_row" flag,
instead of introducing of "result_is_full" - which was
added in the previous commit.


mysql-test/r/func_gconcat.result:
  Adding test case
mysql-test/t/func_gconcat.test:
  Adding test case
sql/item_sum.cc:
  Adding well_formed_len() call not to cut
      in the middle of a multi-byte character.

1 files changed, 24 insertions, 0 deletions

diff --git a/mysql-test/t/func_gconcat.test b/mysql-test/t/func_gconcat.test
index d51d88d50ef..aebceeedcc3 100644
--- a/mysql-test/t/func_gconcat.test
+++ b/mysql-test/t/func_gconcat.test
@@ -391,6 +391,30 @@ select count(distinct (f1+1)) from t1 group by f1 with rollup;
 drop table t1;
 
 #
+# Bug#23451 GROUP_CONCAT truncates a multibyte utf8 character
+#
+set names utf8;
+create table t1
+(
+  x text character set utf8 not null,
+  y integer not null
+);
+insert into t1 values (repeat('a', 1022), 0), (repeat(_utf8 0xc3b7, 4), 0);
+let $1= 10;
+while ($1)
+{
+  eval set group_concat_max_len= 1022 + $1;
+  --disable_result_log
+  select @x:=group_concat(x) from t1 group by y;
+  --enable_result_log
+  select @@group_concat_max_len, length(@x), char_length(@x), right(@x,12), right(HEX(@x),12);
+  dec $1;
+}
+drop table t1;
+set group_concat_max_len=1024;
+set names latin1;
+
+#
 # Bug#14169 type of group_concat() result changed to blob if tmp_table was used
 #
 create table t1 (f1 int unsigned, f2 varchar(255));