MDEV-30164 System variable for default collationsbb-10.11-bar-collations

This patch adds a way to override default collations
(or "character set collations") for desired character sets.

The SQL standard says:
> Each collation known in an SQL-environment is applicable to one
> or more character sets, and for each character set, one or more
> collations are applicable to it, one of which is associated with
> it as its character set collation.

In MariaDB, character set collations has been hard-coded so far,
e.g. utf8mb4_general_ci has been a hard-coded character set collation
for utf8mb4.

This patch allows to override (globally per server, or per session)
character set collations, so for example, uca1400_ai_ci can be set as a
character set collation for Unicode character sets
(instead of compiled xxx_general_ci).

The array of overridden character set collations is stored in a new
(session and global) system variable @@character_set_collations and
can be set as a comma separated list of charset=collation pairs, e.g.:

SET @@character_set_collations='utf8mb3=uca1400_ai_ci,utf8mb4=uca1400_ai_ci';

The variable is empty by default, which mean use the hard-coded
character set collations (e.g. utf8mb4_general_ci for utf8mb4).

The variable can also be set globally by passing to the server startup command
line, and/or in my.cnf.

1 files changed, 18 insertions, 8 deletions

diff --git a/sql/handler.h b/sql/handler.h
index 77c77c83c0f..6d35d6fd953 100644
--- a/sql/handler.h
+++ b/sql/handler.h
@@ -2347,32 +2347,42 @@ struct Table_specification_st: public HA_CREATE_INFO,
     convert_charset_collation.init();
   }
 
-  bool add_table_option_convert_charset(CHARSET_INFO *cs)
+  bool add_table_option_convert_charset(Charset_collation_map_st::Used *used,
+                                        const Charset_collation_map_st &map,
+                                        CHARSET_INFO *cs)
   {
     // cs can be NULL, e.g.: ALTER TABLE t1 CONVERT TO CHARACTER SET DEFAULT;
     used_fields|= (HA_CREATE_USED_CHARSET | HA_CREATE_USED_DEFAULT_CHARSET);
     return cs ?
-      convert_charset_collation.merge_exact_charset(Lex_exact_charset(cs)) :
+      convert_charset_collation.merge_exact_charset(used, map,
+                                                    Lex_exact_charset(cs)) :
       convert_charset_collation.merge_charset_default();
   }
-  bool add_table_option_convert_collation(const Lex_extended_collation_st &cl)
+  bool add_table_option_convert_collation(Charset_collation_map_st::Used *used,
+                                          const Charset_collation_map_st &map,
+                                          const Lex_extended_collation_st &cl)
   {
     used_fields|= (HA_CREATE_USED_CHARSET | HA_CREATE_USED_DEFAULT_CHARSET);
-    return convert_charset_collation.merge_collation(cl);
+    return convert_charset_collation.merge_collation(used, map, cl);
   }
 
-  bool add_table_option_default_charset(CHARSET_INFO *cs)
+  bool add_table_option_default_charset(Charset_collation_map_st::Used *used,
+                                        const Charset_collation_map_st &map,
+                                        CHARSET_INFO *cs)
   {
     // cs can be NULL, e.g.:  CREATE TABLE t1 (..) CHARACTER SET DEFAULT;
     used_fields|= HA_CREATE_USED_DEFAULT_CHARSET;
     return cs ?
-      default_charset_collation.merge_exact_charset(Lex_exact_charset(cs)) :
+      default_charset_collation.merge_exact_charset(used, map,
+                                                    Lex_exact_charset(cs)) :
       default_charset_collation.merge_charset_default();
   }
-  bool add_table_option_default_collation(const Lex_extended_collation_st &cl)
+  bool add_table_option_default_collation(Charset_collation_map_st::Used *used,
+                                          const Charset_collation_map_st &map,
+                                          const Lex_extended_collation_st &cl)
   {
     used_fields|= HA_CREATE_USED_DEFAULT_CHARSET;
-    return default_charset_collation.merge_collation(cl);
+    return default_charset_collation.merge_collation(used, map, cl);
   }
 
   bool resolve_to_charset_collation_context(THD *thd,