Fix for bug#50946: fast index creation still seems to copy the table

Problem: ALTER TABLE ADD INDEX may lead to table copying if there's
numeric field(s) with non-default display width modificator specified.

Fix: compare numeric field's storage lenghts when we decide whether 
they can be considered 'equal' for table alteration purposes.


mysql-test/r/error_simulation.result:
  Fix for bug#50946: fast index creation still seems to copy the table
    - test result.
mysql-test/t/error_simulation.test:
  Fix for bug#50946: fast index creation still seems to copy the table
    - test case.
sql/field.cc:
  Fix for bug#50946: fast index creation still seems to copy the table
    - check numeric field's pack lengths instead of it's display lenghts
  comparing fields equality for table alteration purposes.
sql/sql_table.cc:
  Fix for bug#50946: fast index creation still seems to copy the table
    - check compare_tables() result for testing purposes.

1 files changed, 7 insertions, 0 deletions

diff --git a/sql/sql_table.cc b/sql/sql_table.cc
index ad72cab664e..1101be67d5e 100644
--- a/sql/sql_table.cc
+++ b/sql/sql_table.cc
@@ -6922,6 +6922,13 @@ view_err:
                        &candidate_key_count))
       goto err;
    
+    DBUG_EXECUTE_IF("alter_table_only_metadata_change", {
+      if (need_copy_table_res != ALTER_TABLE_METADATA_ONLY)
+        goto err; });
+    DBUG_EXECUTE_IF("alter_table_only_index_change", {
+      if (need_copy_table_res != ALTER_TABLE_INDEX_CHANGED)
+        goto err; });
+   
     if (need_copy_table == ALTER_TABLE_METADATA_ONLY)
       need_copy_table= need_copy_table_res;
   }