Integrity constraint violation: 1052 Column 'created_at' in where clause is ambiguous

When trying to filter sales order grid with From and To dates it was redirecting to dashboard.after that again i tried to open sales order grind it is generating reports in reports file it showing.

"Integrity constraint violation: 1052 Column 'created_at' in where clause is ambiguous"
means it is finding a another created_at field. because when we adding or joining the other table then it has also a field named as created_at. So below is the  solution for this error.

magento that created_at is of the main_table not of my custom table.

Find the below code in the sales order grid.php file.

$this->addColumn('created_at', array(

           'header' => Mage::helper('sales')->__('Purchased On'),

            'index' => 'created_at',

            'type' => 'datetime',

            'width' => '100px',

        ));

just replace the code with below one.

 $this->addColumn('created_at', array(

'header' => Mage::helper('sales')->__('Purchased On'),

'index' => 'created_at',

'type' => 'datetime',

'width' => '100px',

'filter_index' => 'main_table.created_at',

));

what’s the use of the following line, here created_at column of sales order grid find created_at from the main the collection .But we are getting twice created_at in the collection.So i have added the following line that this created_at is of the main table sales_flat_order not of the other table.

That’s the Solution to solve issue...