Query in function not using index...

Hello,
I need some help with a query inside a function. The table has 31M rows
in it (us streets), and a select statement takes 10ms when using an index
built for the query...

But, when the same query is in a function and uses a variable the index
isn't used and the query takes a few minutes.

Here is the query:

DECLARE
v_cntr INTEGER;
v_streetName VARCHAR := 'wynn%';
v_addr INTEGER := 307;
BEGIN

SELECT count(0) into v_cntr FROM tiger_geocode_roads r
left join placecu p on r.place=p.placei
join state_lookup s on r.state=s.fips
WHERE lower(r.fename::text) like 'wynn%'
AND r.gadd >= v_addr
AND r.ladd <= v_addr
AND fename IS NOT NULL
AND gadd IS NOT NULL
AND ladd IS NOT NULL;

This version comes back in 10ms, but the following takes several minutes:

DECLARE
v_cntr INTEGER;
v_streetName VARCHAR := 'wynn%';
v_addr INTEGER := 307;
BEGIN

SELECT count(0) into v_cntr FROM tiger_geocode_roads r
left join placecu p on r.place=p.placei
join state_lookup s on r.state=s.fips
WHERE lower(r.fename::text) like v_streetName
AND r.gadd >= v_addr
AND r.ladd <= v_addr
AND fename IS NOT NULL
AND gadd IS NOT NULL
AND ladd IS NOT NULL;

Our index looks like:

CREATE INDEX tiger_geocode_roads_lower_fename_addr
ON tiger_geocode_roads
USING btree
(lower(fename::text), gadd, ladd)
WHERE fename IS NOT NULL AND gadd IS NOT NULL AND ladd IS NOT NULL;

Any idea why using a variable v_streetName instead of a string 'wynn%'
behaves differently?

Thanks,

John

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