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MDEV-30164 System variable for default collations

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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.
This commit is contained in:
Alexander Barkov
2022-12-14 18:46:27 +04:00
parent 584c2351de
commit 75f25e4ca7
59 changed files with 2228 additions and 111 deletions
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2
sql/sql_class.cc
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@@ -637,7 +637,7 @@ THD::THD(my_thread_id id, bool is_wsrep_applier)
protocol_text(this), protocol_binary(this), initial_status_var(0),
m_current_stage_key(0), m_psi(0),
in_sub_stmt(0), log_all_errors(0),
binlog_unsafe_warning_flags(0), used(0),
binlog_unsafe_warning_flags(0),
current_stmt_binlog_format(BINLOG_FORMAT_MIXED),
bulk_param(0),
table_map_for_update(0),