lab optimization

labsearch.sql

SET @dist = 20;
SET @latDist = @dist / 69.172;
SELECT zip_codes.*
FROM labs
JOIN zip_codes ON zip_codes.zip_code=labs.zip_code COLLATE utf8_unicode_ci
WHERE zip_codes.zip_code BETWEEN 70000 AND 79999
	AND labs.latitude < zip_codes.latitude + @latDist
    AND labs.latitude > zip_codes.latitude - @latDist
    AND SQRT(
        POW(69.1 * (labs.latitude - zip_codes.latitude), 2) +
        POW(69.1 * (zip_codes.longitude - labs.longitude) * COS(labs.latitude / 57.3), 2)
    ) <= @dist;