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I guess I did not articulate my reasons for suggesting removal of index support for 'long varchar for bit data' completely.
1) Long varchar types are not comparable... If they are not comparable, it should not be possible to use them in GROUP BY, ORDER BY or allow regular B-Tree indexes.
2) Also, long varchar types tend to be long in size and hence the regular B-Tree mechanism is not a suitable way to index them. Dan also mentioned they become ineffective for keys longer than half a page size.
It should not be possible to create an index on 'long varchar for bit data' datatypes. Derby currently doesn't allow creating indexes on 'long varchar' datatypes and the same should apply for it's bit data equivalent too.
ij> create table longchar ( i int, c long varchar);
0 rows inserted/updated/deleted
ij> create index longIdx on longchar(c);
ERROR X0X67: Columns of type 'LONG VARCHAR' may not be used in CREATE INDEX, ORD
ER BY, GROUP BY, UNION, INTERSECT, EXCEPT or DISTINCT statements because compari
sons are not supported for that type.
ij> create table longcharBitData ( i int, c long varchar for bit data);
0 rows inserted/updated/deleted
ij> create index longIdx on longcharBitData(c);
0 rows inserted/updated/deleted
Derby also seems to allow GROUP BY and/or ORDER BY on LONG VARCHAR FOR BIT DATA types. I believe this is incorrect too.
select c from longcharBitData group by c;
C
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0 rows selected
ij> select c from longcharBitData group by c order by c;
C
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0 rows selected