You should be able to do the same thing with an inner join, like this:
SELECT
B.calendar_DT AS dayMov,
A.countries,
A.regions,
'variable' AS validity,
A.name,
A.desc,
'' AS mode
FROM DaysMov A
INNER JOIN Calendar B ON B.year_id = @selYear AND B.month_of_year = A.calMonth AND B.day_of_week = A.calDay AND (B.day_of_month BETWEEN A.calFrom AND A.calTill)
WHERE A.mode = ''
This query will not produce a row when Calendar
does not have a match on the specified condition. Assuming that the query from your post has worked (except that it produced some rows that you did not want) the query above shouldn't produce additional rows, because the subquery on the same condition returned at most a single result.