Try to filter in SQL
let Source = Sql.Database("ericvm2", "testdb", [Query="select S1_DATE, Users from F_googleSessionInformation where s1_date>'"&Date.ToText(defaultDate,"yyyyMMdd")&"'"]) in Source
Or in Power Query
let Source = Sql.Database("ericvm2", "testdb", [Query="select S1_DATE, Users from F_googleSessionInformation"]), filtered = Table.SelectRows(Source, each([S1_Date] > defaultDate )) in Source