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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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18
sql/sql_type.cc
View File

@ -2718,7 +2718,9 @@ Type_handler::Column_definition_set_attributes(THD *thd,
column_definition_type_t type)
const
{
def->set_charset_collation_attrs(attr.charset_collation_attrs());
def->set_charset_collation_attrs(thd,
thd->variables.character_set_collations,
attr.charset_collation_attrs());
def->set_length_and_dec(attr);
return false;
}
@ -3026,7 +3028,9 @@ bool Type_handler_null::
*derived_attr)
const
{
def->prepare_charset_for_string(derived_attr);
def->prepare_charset_for_string(thd,
thd->variables.character_set_collations,
derived_attr);
def->create_length_to_internal_length_null();
return false;
}
@ -3108,7 +3112,10 @@ bool Type_handler_typelib::
*derived_attr)
const
{
return def->prepare_charset_for_string(derived_attr) ||
return def->prepare_charset_for_string(thd,
thd->variables.
character_set_collations,
derived_attr) ||
def->prepare_stage1_typelib(thd, mem_root, type);
}
@ -3122,7 +3129,10 @@ bool Type_handler_string_result::
*derived_attr)
const
{
return def->prepare_charset_for_string(derived_attr) ||
return def->prepare_charset_for_string(thd,
thd->variables.
character_set_collations,
derived_attr) ||
def->prepare_stage1_string(thd, mem_root);
}