I'm trying to count customers who have received services by ZIP code, but I want to count each customer only once even though customers may have received services on multiple dates, and therefore appear in the table multiple times. There *is* a separate customers table, but because of dirty data, I cannot rely on it.
The best I can come up with is:
SELECT zip, count(*) AS count_serviced FROM (SELECT DISTINCT zip, id FROM customer_service_date) a GROUP BY zip ;
The table (with some irrelevant fields dropped) is:
CREATE TABLE customer_service_date ( id integer, address character varying, city character varying, state character varying, zip character varying, service_date date ) ;
The table is missing a primary key field, but it would be (id, service_date) if it had one.
Any suggestions to improve this?
Thanks, --Lee
-- Lee Hachadoorian PhD Student, Geography Program in Earth & Environmental Sciences CUNY Graduate Center
