How to reference TSQL calculated field from outer query in subquery

Question

Not sure how to code the following in T-SQL:

Select 
    RunDate, 
    Lead(RunDate) Over(Order By Rundate) NextRunDate,
    (Select count(*) 
     From DetailTable
     Where DetailTable.EventDate <= NextRunDate) as Cnt
From   
    RunDates

The use of NextRunDate in the subquery throws an

Invalid column name

error, which makes sense. But how to reference that outer variable? Thanks!

Answer 1

You can nest your query leaving out the subquery in another query, that then includes the subquery.

SELECT x.rundate,
       (SELECT count(*)
               FROM detailtable d
               WHERE d.eventdate <= x.nextrundate) cnt
       FROM (SELECT r.rundate, 
                    lead(r.rundate) OVER (ORDER BY r.rundate) nextrundate
                    FROM rundates r) x;