Radek Strnad napsal(a):
<snip>
I'm thinking of dividing the problem into two parts - in beginning
pg_collation will contain two functions. One will have hard-coded rules
for these basic collations (SQL_CHARACTER, GRAPHIC_IRV, LATIN1, ISO8BIT,
UCS_BASIC). It will compare each string character bitwise and guarantee
that the implementation will meet the SQL standard implemented in
PostgreSQL.
Second one will allow the user to use installed system locales. The set
of these collations will obviously vary between systems. Catalogs will
contain encoding and collation for calling the system locale function.
This will allow us to use collations such as en_US.utf8, cs_CZ.iso88592
etc. if they will be availible.
We will also need to change the way how strings are compared. Regarding
the set database collation the right function will be used.
http://doxygen.postgresql.org/varlena_8c.html#4c7af81f110f9be0bd8eb2bd99525675
This design will make possible switch to ICU or any other implementation
quite simple and will not cause any major rewriting of what I'm coding
right now.
Collation function is main point here. How you mentioned one will be only
wrapper about strcmp and second one about strcoll. (maybe you need four -
char/wchar) Which function will be used it is defined in pg_collation catalog by
CREATE COLLATION command. But you need specify name of locale for system
locales. It means you need attribute for storing locale name.
<snip>
CATALOG(pg_collations, ###)
{
NameData colname; /* collation name */
Oid colschema; /* collation schema */
bool colpadattribute; /* pad attribute */
bool colcasesensitive; /* case sensitive */
bool colaccent; /* accent sensitive */
regproc colfunc; /* used collation function */
Oid colrepertoire; /* collation repertoire */
} FormData_pg_collations;
It would be good to send list of new and modified SQL commands (like CREATE
COLLATION) for wide discussion.
Zdenek
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