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< operator for user-defined types

From: Teodor Sigaev <teodor(at)sigaev(dot)ru>
To: Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: < operator for user-defined types
Date: 2004-03-25 14:44:39
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Lists: pgsql-hackers
I got several suggestions to include ordering operator for tsvector to aim 
grouping, union and except etc.

I wrote silly comparing function (byte to byte with some optimizations), but I 
wondered that for using operator < in order clause its need to declate B-tree 
opclass for type:

regression=# select  a from test_tsvector order by a;
ERROR:  could not identify an ordering operator for type tsvector
HINT:  Use an explicit ordering operator or modify the query.

I see in
backend/utils/cache/typcache.c near line 169:

         if ((flags & TYPECACHE_LT_OPR) && typentry->lt_opr == InvalidOid)
                 if (typentry->btree_opc != InvalidOid)
                         typentry->lt_opr = 
get_opclass_member(typentry->btree_opc,InvalidOid, BTLessStrategyNumber);

So, I must declare b-tree opclass for tsvector. Why?
My supposition is to guarantee that operator < is really 'less-than' one. Is it?

Teodor Sigaev                                  E-mail: teodor(at)sigaev(dot)ru


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