Slow update SQL

I'm experiencing a very slow query. The table contains 611,564 rows of data. I vaccumed the table:<br /><br /> VACUUM
ANALYZEncccr10;<br /><br /> SELECT count(*) FROM ncccr10;<br /> count<br /> --------<br /> 611564<br /> (1 row)<br
/><br/> When I try to analyze the query plan with:<br /><br /> EXPLAIN ANALYZE<br /> UPDATE ncccr10<br /> SET key =
facilityno||'-'||<br/> lastname||'-'||<br /> sex||'-'||<br /> ssno||'-'||<br /> birthdate||'-'||<br />
primarysit||'-'||<br/> dxdate||'-'||<br /> morphology3<br /> WHERE date_part('year',dxdate) > '2000';<br /><br />
Thequery just never finishes (even 1 hour later). The colum key100 is indexed, and I'm setting the value of this<br />
columnfrom other columns. Why is this so slow? <br /><br />