MDEV-3798: EXPLAIN UPDATE/DELETE

- Produce correct `key_len` when type=index.

1 files changed, 4 insertions, 1 deletions

diff --git a/sql/sql_delete.cc b/sql/sql_delete.cc
index 00193800b93..7f58526d174 100644
--- a/sql/sql_delete.cc
+++ b/sql/sql_delete.cc
@@ -158,8 +158,11 @@ void Update_plan::save_explain_data_intern(Explain_query *query,
     if (index != MAX_KEY)
     {
       explain->key_str.append(table->key_info[index].name);
+      char buf[64];
+      size_t length;
+      length= longlong10_to_str(table->key_info[index].key_length, buf, 10) - buf;
+      explain->key_len_str.append(buf, length);
     }
-    // key_len stays NULL
   }
   explain->rows= scanned_rows;