sql优化——union

1:对于多业务多条件的查询，可以分开查询，然后用union整合，这样能提升速度

SELECT * FROM (
SELECT c.* FROM
company_to_category t, company c, message m
WHERE t.cat_id IN (1045340) AND t.company_id = c.company_id AND c.company_id = m.receiver AND c.company_id =2626156
UNION
SELECT c.* FROM
company_to_category t, company c, company_favorite f
WHERE t.cat_id IN (1045340) AND t.company_id = c.company_id AND (c.company_id=f.fid AND f.type='C'))t LIMIT 0,5