PHP/SQL - Return boolean result from SQL query between two dates

Question

I've been asked to build a scheduler to display special offers on a website based on start/end dates. Part of that is to conditionally display a link to the page if there is a valid offer in place. But I'm completely at a loss.

The following query fetches any current offers which fall within the correct dates:

$now = date('Y-m-j');
$sql = "SELECT * FROM sample WHERE date_from <= '".$now."' AND date_to > '".$now."'";

I've not been able to develop this query to return a TRUE/FALSE value (which I need for the existing navigational structure - created by another developer). There've been some posts stating to use EXISTS() or SELECT CASE WHEN EXISTS() on the existing query, followed by THEN/ELSE for the output. But after hours of trying to crack this I've only managed to garner errors.

I know it's probably possible to work around this, but I want to return a boolean from the SQL query itself.

Answer 1

case should work:

select
CASE 
  WHEN date_from <= '".$now."' AND date_to > '".$now."' THEN 'TRUE'
  ELSE 'FALSE'
END

from yourtable 

perhaps better

SELECT exists (
  SELECT * FROM sample WHERE date_from <= '".$now."' AND date_to > '".$now."') as BOO

BOO will be 1 if there is a match

Answer 2

PHP database queries return resources to the result of the query. The result is an array or object of elements returned by the select statement.

If you want to return a boolean from the sql query itself. Then you must change your * (asterisk) to something that is a boolean.

Depending on the database you are using, the exact syntax and functionality available changes. But let's assume microsoft sql or postgres..

Postgres:

$sql = "SELECT (count(*)>0) as bool_result FROM sample WHERE date_from <= '".$now."' AND date_to > '".$now."'";

Microsoft SQL:

$sql = "SELECT (case when count(*)>0 then 1 else 0 end) as int_result FROM sample WHERE date_from <= '".$now."' AND date_to > '".$now."'";

Microsoft SQL uses the tiny int or bit for booleans. So there is no way to return a strictly speaking "Boolean". Hence the case when structure for the 1 or 0 from the boolean comparison.

If you want to know if ANY rows are returned and you care not the result set, then maybe mssql_num_rows or pg_num_rows is more your answer. Both return the number of rows in the query result set. You could then compare that to being equal to 0 or 1.

This is about as close to an answer you can get without supplying a code example and more details.

Here's an example:

$sql = "SELECT * FROM sample WHERE date_from <= '".$now."' AND date_to > '".$now."'";
$res = pg_query($sql);
if( pg_num_rows($res) > 0 ) 
    ShowNav();