int8 index isn't used for query against number

Hi,

I was having trouble with what seemed to be very slow access to a
table I had created. When I used EXPLAIN to clarify matters, it
seemed that my query required quotes around the parameter in order to
get the use of my index; otherwise a sequential scan is used (the
table is over 2 million rows so that was taking too long...).

Is this "expected" behavior and, if so, how do I know when to use
quotes around query parameters?

System:
Postgresql 6.5.1 with patches for vacuum and unique index
Irix 6.5

Thanks,
Mark

=========================================================================
CREATE TABLE Seq (
Contig_ID int8 PRIMARY KEY,
Contig_Accession int8 UNIQUE NOT NULL,
FileID smallint NOT NULL,
ByteOffset int8 NOT NULL, -- Use ftell64() under IRIX
SeqLength int NOT NULL,
FOREIGN KEY (FileID) REFERENCES File
ON UPDATE CASCADE ON DELETE CASCADE
);

db=> \d Seq
Table = seq
+----------------------------------+----------------------------------+-------+
| Field | Type | Length|
+----------------------------------+----------------------------------+-------+
| contig_id | int8 not null | 8 |
| contig_accession | int8 not null | 8 |
| fileid | int2 not null | 2 |
| byteoffset | int8 not null | 8 |
| seqlength | int4 not null | 4 |
+----------------------------------+----------------------------------+-------+
Indices: seq_contig_accession_key
seq_pkey

db=> select count(*) from seq;
count
-------
2370400
(1 row)

-- Without quotes, no Index scan; very slow
db=> EXPLAIN
db-> SELECT FileID, Contig_Accession, ByteOffset, SeqLength FROM Seq S
db-> WHERE Contig_Accession=6739795;
NOTICE: QUERY PLAN:

Seq Scan on seq s (cost=105160.20 rows=1 width=22)

EXPLAIN

-- With quotes, index scan and almost instantaneous responce.
db=> explain
db-> SELECT FileID, Contig_Accession, ByteOffset, SeqLength FROM Seq S
db-> WHERE Contig_Accession='6739795';
NOTICE: QUERY PLAN:

Index Scan using seq_contig_accession_key on seq s (cost=2.05 rows=1 width=22)

EXPLAIN

====================================================================

--
Mark Dalphin email: mdalphin(at)amgen(dot)com
Mail Stop: 29-2-A phone: +1-805-447-4951 (work)
One Amgen Center Drive +1-805-375-0680 (home)
Thousand Oaks, CA 91320 fax: +1-805-499-9955 (work)