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在业务查询中经常会出现【过滤出最新一条记录】的需求，下面写一个用【NOT EXISTS】实现的小例子记录一下： SELECT t1.unit_id, IFNULL( COUNT(distinct t.person_phr_code ), 0 ) AS visit_person_num, IFNULL( COUNT(distinct CASE WHEN t.avg_sbp < 130 AND t.avg_dbp < 80 THEN t.person_phr_code ELSE NULL END ), 0 ) AS person_num_80_130, IFNULL( COUNT(distinct CASE WHEN t.avg_sbp < 140 AND t.avg_dbp < 90 THEN t.person_phr_code ELSE NULL END ), 0 ) AS person_num_90_140 FROM yida_historical_visit_info t, yida_person_basic_info t1 WHERE t.person_phr_code = t1.person_phr_code AND NOT EXISTS ( SELECT 1 FROM `yida_historical_visit_info` n WHERE t.person_phr_code = n.person_phr_code AND t.visit_date < n.visit_date) GROUP BY t1.unit_id