MySQL DateDiff in Where clause?

Question

We are using Yii Framework and have created a search form to include the following DatePicker widge:

<?php echo $form->labelEx($model, 'availability_start_date');?>
        <?php 
        Yii::import('zii.widgets.jui.CJuiDatePicker');
        $this->widget('zii.widgets.jui.CJuiDatePicker', array(
            'name'=>'stattDate',
            'options'=>array(
                'showAnim'=>'fold',
            ),
            'htmlOptions'=>array(
                'style'=>'height:20px;'
            )
        ));
        ?>

This widget needs to be used to search for users who have an availability_start_date +/- 2 days from the value specified in the above widget.

Our UserController has the following join logic:

if ($search_frm['availability_start_date']){
                    $join .= ' LEFT JOIN user_availability_start_date usd on u.id = usd.id';
                    $where .= 'AND usd.availability_start_date >= '.$search_frm
                ['availability_start_date'];
                }

Currently the logic in the WHERE clause just asks for a match where the availability_start_date is greater than or equal to the widget's value.

How do I modify the above WHERE clause to select those records where the widget's value is +/- 2 days different than the availability_start_date value?

UPDATE: I've revised the where clause to read as follows:

if ($search_frm['availability_start_date']){
                    $join .= ' LEFT JOIN user_availability_start_date usd on u.id = usd.id';
                    $where .= ' AND usd.availability_start_date >= DATE_ADD('.$search_frm.', 
                INTERVAL -2 DAY)
                    AND usd.availability_start_date <= DATE_ADD(' .$search_frm.', INTERVAL 2 DAY)';
                }

Unfortunately, when I test the logic, records are returned that don't meet this criteria. No errors are thrown on the form or page.

Answer 1

DATEDIFF() returns a value in days. For +/- 2 days you will want to use the absolute value ABS() returned by DATEDIFF(), verify that it is <= 2.

$where .= "AND ABS(DATEDIFF(DATE(usd.availability_start_date), DATE('" . $search_frm['availability_start_date'] . "'))) <= 2";

I have also wrapped the arguments to DATEDIFF() in DATE() to truncate off the time portions if they are present. Remove those if they are unnecessary for your application.