常用的一些复杂SQL语句

1.根据表中的birthday统计年龄段人数：

//以下代码表示查询出来后的结果集添加一列字段

cast(‘20以下‘ as char) as age

SELECT COUNT(*) as num,cast(‘20以下‘ as char) as age FROM (SELECT (DATE_FORMAT(NOW(),‘%Y‘)-DATE_FORMAT(birthday,‘%Y‘)) AS age FROM hm_applicant WHERE (DATE_FORMAT(NOW(),‘%Y‘)-DATE_FORMAT(birthday,‘%Y‘)) <= 20) AS A
UNION
SELECT COUNT(*) as num,cast(‘20-40‘ as char) as age FROM (SELECT (DATE_FORMAT(NOW(),‘%Y‘)-DATE_FORMAT(birthday,‘%Y‘)) AS age FROM hm_applicant WHERE (DATE_FORMAT(NOW(),‘%Y‘)-DATE_FORMAT(birthday,‘%Y‘)) > 20 AND (DATE_FORMAT(NOW(),‘%Y‘)-DATE_FORMAT(birthday,‘%Y‘)) <= 40) AS A
UNION
SELECT COUNT(*) as num,cast(‘40-60‘ as char) as age FROM (SELECT (DATE_FORMAT(NOW(),‘%Y‘)-DATE_FORMAT(birthday,‘%Y‘)) AS age FROM hm_applicant WHERE (DATE_FORMAT(NOW(),‘%Y‘)-DATE_FORMAT(birthday,‘%Y‘)) > 40 AND (DATE_FORMAT(NOW(),‘%Y‘)-DATE_FORMAT(birthday,‘%Y‘)) <= 60) AS A
UNION
SELECT COUNT(*) as num,cast(‘60-80‘ as char) as age FROM (SELECT (DATE_FORMAT(NOW(),‘%Y‘)-DATE_FORMAT(birthday,‘%Y‘)) AS age FROM hm_applicant WHERE (DATE_FORMAT(NOW(),‘%Y‘)-DATE_FORMAT(birthday,‘%Y‘)) > 60 AND (DATE_FORMAT(NOW(),‘%Y‘)-DATE_FORMAT(birthday,‘%Y‘)) <= 80) AS A
UNION
SELECT COUNT(*) as num,cast(‘80以上‘ as char) as age FROM (SELECT (DATE_FORMAT(NOW(),‘%Y‘)-DATE_FORMAT(birthday,‘%Y‘)) AS age FROM hm_applicant WHERE (DATE_FORMAT(NOW(),‘%Y‘)-DATE_FORMAT(birthday,‘%Y‘)) > 80) AS A

效果图如下图：