Bug#28925 GROUP_CONCAT inserts wrong separators for a ucs2 column

Problem: separator was not converted to the result character set,
so the result was a mixture of two different character sets,
which was especially bad for UCS2.
Fix: convert separator to the result character set.

mysql-test/r/ctype_ucs.result

@@ -865,4 +865,25 @@ blob	65535	65535
 text	65535	65535
 text	65535	32767
 drop table t1;
+create table t1 (a char(1) character set ucs2);
+insert into t1 values ('a'),('b'),('c');
+select hex(group_concat(a)) from t1;
+hex(group_concat(a))
+0061002C0062002C0063
+select collation(group_concat(a)) from t1;
+collation(group_concat(a))
+ucs2_general_ci
+drop table t1;
+set names latin1;
+create table t1 (a char(1) character set latin1);
+insert into t1 values ('a'),('b'),('c');
+set character_set_connection=ucs2;
+select hex(group_concat(a separator ',')) from t1;
+hex(group_concat(a separator ','))
+612C622C63
+select collation(group_concat(a separator ',')) from t1;
+collation(group_concat(a separator ','))
+latin1_swedish_ci
+drop table t1;
+set names latin1;
 End of 5.0 tests

mysql-test/r/ctype_ucs2_def.result

@@ -7,3 +7,11 @@ character_set_server	ucs2
 DROP TABLE IF EXISTS t1;
 create table t1 (a int);
 drop table t1;
+End of 4.1 tests
+create table t1 (a char(1) character set latin1);
+insert into t1 values ('a'),('b'),('c');
+select hex(group_concat(a)) from t1;
+hex(group_concat(a))
+612C622C63
+drop table t1;
+End of 5.0 tests

mysql-test/t/ctype_ucs.test

@@ -594,4 +594,22 @@ select data_type, character_octet_length, character_maximum_length
   from information_schema.columns where table_name='t1';
 drop table t1;
 
+#
+# Bug#28925 GROUP_CONCAT inserts wrong separators for a ucs2 column
+#
+create table t1 (a char(1) character set ucs2);
+insert into t1 values ('a'),('b'),('c');
+select hex(group_concat(a)) from t1;
+select collation(group_concat(a)) from t1;
+drop table t1;
+
+set names latin1;
+create table t1 (a char(1) character set latin1);
+insert into t1 values ('a'),('b'),('c');
+set character_set_connection=ucs2;
+select hex(group_concat(a separator ',')) from t1;
+select collation(group_concat(a separator ',')) from t1;
+drop table t1;
+set names latin1;
+
 --echo End of 5.0 tests

mysql-test/t/ctype_ucs2_def.test

@@ -14,3 +14,16 @@ DROP TABLE IF EXISTS t1;
 --enable_warnings
 create table t1 (a int);
 drop table t1;
+
+--echo End of 4.1 tests
+
+#
+# Bug #28925 GROUP_CONCAT inserts wrong separators for a ucs2 column
+# Check that GROUP_CONCAT works fine with --default-character-set=ucs2
+#
+create table t1 (a char(1) character set latin1);
+insert into t1 values ('a'),('b'),('c');
+select hex(group_concat(a)) from t1;
+drop table t1;
+
+--echo End of 5.0 tests

sql/item_sum.cc

@@ -3209,6 +3209,27 @@ Item_func_group_concat::fix_fields(THD *thd, Item **ref)
   null_value= 1;
   max_length= thd->variables.group_concat_max_len;
 
+  uint32 offset;
+  if (separator->needs_conversion(separator->length(), separator->charset(),
+                                  collation.collation, &offset))
+  {
+    uint32 buflen= collation.collation->mbmaxlen * separator->length();
+    uint errors, conv_length;
+    char *buf;
+    String *new_separator;
+
+    if (!(buf= thd->stmt_arena->alloc(buflen)) ||
+        !(new_separator= new(thd->stmt_arena->mem_root)
+                           String(buf, buflen, collation.collation)))
+      return TRUE;
+    
+    conv_length= copy_and_convert(buf, buflen, collation.collation,
+                                  separator->ptr(), separator->length(),
+                                  separator->charset(), &errors);
+    new_separator->length(conv_length);
+    separator= new_separator;
+  }
+
   if (check_sum_func(thd, ref))
     return TRUE;
 

sql/sql_yacc.yy

@@ -5420,8 +5420,11 @@ opt_distinct:
     |DISTINCT   { $$ = 1; };
 
 opt_gconcat_separator:
-    /* empty */        { $$ = new (YYTHD->mem_root) String(",",1,default_charset_info); }
-    |SEPARATOR_SYM text_string  { $$ = $2; };
+    /* empty */
+      {
+        $$= new (YYTHD->mem_root) String(",", 1, &my_charset_latin1);
+      }
+    | SEPARATOR_SYM text_string { $$ = $2; };
 
 
 opt_gorder_clause: