Going off Barand's example, with implode and a bit of string manipulation you can do:
$designation = array ( 'Managing Director', 'Manager', 'Director', 'The Principal', 'Deputy Principal', 'Proprietor', 'Assistant Manager', 'Head Master');
$sql = "SELECT .... FROM mytablename WHERE somecolumn IN('" . str_replace(',', '\', \'', implode(',', $designation)) . "')";
echo $sql;
Output:
SELECT .... FROM mytablename WHERE somecolumn IN('Managing Director', 'Manager', 'Director', 'The Principal', 'Deputy Principal', 'Proprietor', 'Assistant Manager', 'Head Master')
EDIT: This is probably easier to read (replaced single quotes in function with double quotes):
$sql = "SELECT .... FROM mytablename WHERE somecolumn IN('" . str_replace(",", "', '", implode(",", $designation)) . "')";