弱弱地问个sql语句小疑点_Sql Server

弱弱地问个sql语句小问题
update adminInfo set maxOnline = (select count(*) from userInfo where isOnline = 1), maxDate = GETDATE() where maxOnline < (select count(*) from userInfo where isOnline = 1) and adminId = 1

这个语句有两次(select count(*) from userInfo where isOnline = 1) 怎样写只需要查询一次呢？

------解决方案--------------------
在外面定义一个变量不就好了吗
DECLARE @COUNT INT

select @COUNT=count(*) from userInfo where isOnline = 1

update adminInfo set maxOnline = @COUNT, maxDate = GETDATE() where maxOnline < @COUNT and adminId = 1

------解决方案--------------------
定义变量，把查询语句的值赋给变量
------解决方案--------------------

SQL code

declare @count int=select count(*) from userInfo where isOnline = 1update adminInfo set maxOnline = @count, maxDate = GETDATE() where maxOnline <@count  and adminId = 1
------解决方案--------------------
TRY
SQL codeupdate adminInfo set maxOnline = b.total , maxDate = GETDATE() from  (select count(*) total from userInfo where isOnline = 1) b where where maxOnline < b.total  and adminId =  1