课程资料网盘链接:https://pan.baidu.com/s/1-jOwaXWArtv8h21B0-uWGg 提取码:wsra
SQL零基础入门笔记:https://www.mubucm.com/doc/4VC7JuHlj6H
云端数据库安装文档:https://share.mubu.com/doc/rBUGcUie8H
Python安装文档:https://www.mubucm.com/doc/4DJ8YNSNz4F
https://sqlzoo.net/wiki/window_LAG
![](https://img.haomeiwen.com/i946850/1d8857ebc646447b.png)
select
recovered 累计治愈人数
,case when recovered = 1 then 'one' when recovered >1 then 'more' else '0'
end
from covid
where recovered > 0
![](https://img.haomeiwen.com/i946850/910385042c777ce3.png)
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