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((DATE_FORMAT(NOW(),\'%Y\')-DATE_FORMAT(birthday,\'%Y\'))) as value,cast(\'20岁以下\' as char) as name 
            FROM hm_applicant WHERE (DATE_FORMAT(NOW(),\'%Y\')-DATE_FORMAT(birthday,\'%Y\')) <= 20
UNION
SELECT COUNT((DATE_FORMAT(NOW(),\'%Y\')-DATE_FORMAT(birthday,\'%Y\'))) as value,cast(\'20-40岁\' as char) as name 
            FROM hm_applicant WHERE (DATE_FORMAT(NOW(),\'%Y\')-DATE_FORMAT(birthday,\'%Y\')) > 20 AND (DATE_FORMAT(NOW(),\'%Y\')-DATE_FORMAT(birthday,\'%Y\')) <= 40
UNION
SELECT COUNT((DATE_FORMAT(NOW(),\'%Y\')-DATE_FORMAT(birthday,\'%Y\'))) as value,cast(\'40-60岁\' as char) as name  
        FROM hm_applicant WHERE (DATE_FORMAT(NOW(),\'%Y\')-DATE_FORMAT(birthday,\'%Y\')) > 40 AND (DATE_FORMAT(NOW(),\'%Y\')-DATE_FORMAT(birthday,\'%Y\')) <= 60
UNION
SELECT COUNT((DATE_FORMAT(NOW(),\'%Y\')-DATE_FORMAT(birthday,\'%Y\'))) as value,cast(\'60-80岁\' as char) as name 
        FROM hm_applicant WHERE (DATE_FORMAT(NOW(),\'%Y\')-DATE_FORMAT(birthday,\'%Y\')) > 60 AND (DATE_FORMAT(NOW(),\'%Y\')-DATE_FORMAT(birthday,\'%Y\')) <= 80
UNION
SELECT COUNT((DATE_FORMAT(NOW(),\'%Y\')-DATE_FORMAT(birthday,\'%Y\'))) as value,cast(\'80岁以上\' as char) as name 
    FROM hm_applicant WHERE (DATE_FORMAT(NOW(),\'%Y\')-DATE_FORMAT(birthday,\'%Y\')) > 80

效果图如下图：