[Today]-15 filter not working on external list

Question

I have an external list which is getting data from SQL Server. The table structure is as follows:

Name
InsertDate

Where InsertDate is the date when record was inserted.

I am trying to show only those records which were entered during last 15 days. So I used the following filter in that external list's view but still it returns all records.

where InsertDate is greater than or equal to [Today]-15

I have checked that all records in SQL Server have InsertDate set to 2013-10-10 which is basically 10 October 2013 and today is 19 Nov 2013 so basically [Today]-15 will return 2013-11-04 so it should not show any record as they were entered in October.

Answer 1

I did some experimentation a while back involving CAML operators with various field types, and it seems that all external columns get passed back to SP as Strings. You can use DateValue(InsertDate) in your formula to get it as a date (possibly using a calculated column if needed).