How to select data according to specific dates

Question

I am using QGIS Essen version 2.14.1, and I am trying to select specific data according to dates in the field calculator:

I am using the following formula but the system is telling me: syntax error, unexpected LE

Here is my formula:

case when 
( "Copy of _4"  > 01/09/2016 and  "Copy of _5" < 18/09/2016)
 then 'Y' else 'N' end

Anyone know where I am going wrong?

Answer 1

I post my response to your comment as a real answer for readability purpose.

Your function should probably look like:

case when 
( to_date("Copy of _4") > '2016-09-01' and to_date("Copy of _5") < '2016-09-18')
 then 'Y' else 'N' end

This assumes that both "Copy of _4" and "Copy of _5" contain dates with the following format: YYYY-MM-DD (it probably won't work otherwise).

Answer 2

Slightly improved version of ArMoraer's answer:

CASE WHEN
to_date(substr("Copy of _4", 7,5) + '-' + substr("Copy of _4", 4,2)  + '-' + substr("Copy of _4", 1,2)) > to_date('2016-09-01')
AND
to_date(substr("Copy of _5", 7,5) + '-' + substr("Copy of _5", 4,2)  + '-' + substr("Copy of _5", 1,2)) > to_date('2016-09-18')
THEN 'y' ELSE 'N' END

Be aware that this is rather messy and only works for the exact date format you're using here.