MDEV-18899: Server crashes in Field::set_warning_truncated_wrong_value

To fix the crash there we need to make sure that the
server while storing the statistical values in statistical tables should do it
in a multi-byte safe way.
Also there is no need to throw warnings if there is truncation while storing
values from statistical fields.

2 files changed, 12 insertions, 5 deletions

diff --git a/sql/field.cc b/sql/field.cc
index 080cf34c76d..0621015c0e4 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -7027,8 +7027,11 @@ Field_longstr::check_string_copy_error(const String_copier *copier,
   if (!(pos= copier->most_important_error_pos()))
     return FALSE;
 
-  convert_to_printable(tmp, sizeof(tmp), pos, (end - pos), cs, 6);
-  set_warning_truncated_wrong_value("string", tmp);
+  if (!is_stat_field)
+  {
+    convert_to_printable(tmp, sizeof(tmp), pos, (end - pos), cs, 6);
+    set_warning_truncated_wrong_value("string", tmp);
+  }
   return TRUE;
 }
 
diff --git a/sql/sql_statistics.cc b/sql/sql_statistics.cc
index b5811c683e8..0a51346adb2 100644
--- a/sql/sql_statistics.cc
+++ b/sql/sql_statistics.cc
@@ -1060,7 +1060,9 @@ public:
           else
           {
             table_field->collected_stats->min_value->val_str(&val);
-            stat_field->store(val.ptr(), val.length(), &my_charset_bin);
+            uint32 length= Well_formed_prefix(val.charset(), val.ptr(),
+                           MY_MIN(val.length(), stat_field->field_length)).length();
+            stat_field->store(val.ptr(), length, &my_charset_bin);
           }
           break;
         case COLUMN_STAT_MAX_VALUE:
@@ -1069,7 +1071,9 @@ public:
           else
           {
             table_field->collected_stats->max_value->val_str(&val);
-            stat_field->store(val.ptr(), val.length(), &my_charset_bin);
+            uint32 length= Well_formed_prefix(val.charset(), val.ptr(),
+                            MY_MIN(val.length(), stat_field->field_length)).length();
+            stat_field->store(val.ptr(), length, &my_charset_bin);
           }
           break;
         case COLUMN_STAT_NULLS_RATIO:
@@ -3059,7 +3063,7 @@ int read_statistics_for_table(THD *thd, TABLE *table, TABLE_LIST *stat_tables)
       }
     }
   }
-      
+
   table->stats_is_read= TRUE;
 
   DBUG_RETURN(0);