MDEV-20190 Instant operation fails when add column and collation change on non-indexed column

We must relax too strict debug assertions. For latin1_swedish_ci,
mtype=DATA_CHAR or mtype=DATA_VARCHAR will be used instead of
mtype=DATA_MYSQL or mtype=DATA_VARMYSQL. Likewise, some changes of
dtype_get_charset_coll() do not affect the data type encoding,
but only any indexes that are defined on the column.

Charset::same_encoding(): Check whether two charset-collations have
the same character set encoding.

dict_col_t::same_encoding(): Check whether two character columns
have the same character set encoding.

dict_col_t::same_type(): Check whether two columns have a compatible
data type encoding.

dict_col_t::same_format(), dict_table_t::instant_column(): Do not
compare mtype or the charset-collation of prtype directly.
Rely on dict_col_t::same_type() instead.

dtype_get_charset_coll(): Narrow the return type to uint16_t.

This is a refined version of a fix that was developed by
Thirunarayanan Balathandayuthapani.

1 files changed, 5 insertions, 1 deletions

diff --git a/sql/sql_string.h b/sql/sql_string.h
index 605480461f1..aad5314a973 100644
--- a/sql/sql_string.h
+++ b/sql/sql_string.h
@@ -3,7 +3,7 @@
 
 /*
    Copyright (c) 2000, 2013, Oracle and/or its affiliates.
-   Copyright (c) 2008, 2018, MariaDB Corporation.
+   Copyright (c) 2008, 2019, MariaDB Corporation.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -164,6 +164,10 @@ public:
   {
     swap_variables(CHARSET_INFO*, m_charset, other.m_charset);
   }
+  bool same_encoding(const Charset &other) const
+  {
+    return !strcmp(m_charset->csname, other.m_charset->csname);
+  }
   /*
     Collation name without the character set name.
     For example, in case of "latin1_swedish_ci",