https://docs.microsoft.com/zh-cn/sql/?view=sql-server-2017
一百教程介绍关于sqlserver的教程 https://www.yiibai.com/sqlserver/sql-server-aggregate-functions.html
https://docs.microsoft.com/zh-cn/sql/?view=sql-server-2017
一百教程介绍关于sqlserver的教程 https://www.yiibai.com/sqlserver/sql-server-aggregate-functions.html