Fix Bug #21328 mysqld issues warnings on ALTER CSV table to MyISAM

mysql-test/r/csv.result:
  update result file
mysql-test/r/log_tables.result:
  log_tables test contains alter of a CSV table with
  NULLs which results in warnings. In fact this is how
  the bug noticed. So, now when it is fixed we should
  update result file.
mysql-test/t/csv.test:
  add a test for the bug
storage/csv/ha_tina.cc:
  We should write 0 to the data file in the
  case we meet NULL. CSV does not support
  NULL values internally and we shouldn't
  distinguish them from 0 when writing a row
  (the alternative is to implement full NULL
  support). Otherwise other routines (such as
  Field::check_int() become confused).
  In 5.0 NULLs are stored as zeroes. In 5.1 it
  somehow turned into empty string. Which is wrong.

1 files changed, 4 insertions, 2 deletions

diff --git a/storage/csv/ha_tina.cc b/storage/csv/ha_tina.cc
index f7e5aa9d50c..6a6bc52d6ad 100644
--- a/storage/csv/ha_tina.cc
+++ b/storage/csv/ha_tina.cc
@@ -542,14 +542,16 @@ int ha_tina::encode_quote(byte *buf)
     const char *end_ptr;
 
     /*
-      Write an empty string to the buffer in case of a NULL value.
+      CSV does not support nulls. Write quoted 0 to the buffer. In fact,
+      (*field)->val_str(&attribute,&attribute) would usually return 0
+      in this case but we write it explicitly here.
       Basically this is a safety check, as no one ensures that the
       field content is cleaned up every time we use Field::set_null()
       in the code.
     */
     if ((*field)->is_null())
     {
-      buffer.append(STRING_WITH_LEN("\"\","));
+      buffer.append(STRING_WITH_LEN("\"0\","));
       continue;
     }
     else