版权声明：本文为博主搜索整合文章。 https://blog.csdn.net/weixin_37794901/article/details/79445491
demo：
本人项目的使用的需求场景：
统计每日：会员，会员登入，会员注册，会员活跃，的总数，接口返回的栏位都是total，date，module，只不过模块不一样使用的表和获取数据的字段的不同；（供参考）
<select id="analytics" resultType="map">
<when test="module == 'AMOUNT'"> <!-- 执行的条件-->
SELECT updatedAt,total,'AMOUNT' AS 'module' FROM table1 m
WHERE m.`updatedAt` >= DATE_SUB(CURDATE(),INTERVAL #{interval} DAY)
</when>
<when test="module == 'LOGIN'">
SELECT SUM(d.count) AS 'total','LOGIN' AS 'module' ,d.`updatedAt` FROM table2 d WHERE
d.`action`='LOGIN' and d.`updatedAt` >= DATE_SUB(CURDATE(),INTERVAL #{interval} DAY) GROUP BY DATE_FORMAT(updatedAt,'%Y%M%d')
</when>
<when test="module == 'REGISTER'">
SELECT SUM(d.count) AS 'total', 'REGISTER' AS 'module',d.`updatedAt` FROM table3 d WHERE
d.`action`='REGISTER' and d.`updatedAt` >= DATE_SUB(CURDATE(),INTERVAL #{interval} DAY) GROUP BY DATE_FORMAT(updatedAt,'%Y%M%d')
</when>
<when>...</when>...
</select>