sql语句多条件查询

$sql = "SELECT * FROM 表名 WHERE 1=1";
if($region!=null)
{
$sql .= " AND 字段='$region'";
}

if($hold!=null)
{
$sql .= " AND 字段like '%$hold%' AND 字段<70 AND 字段between 100 and 150";}

$result = mysqli_query($conn,$sql);

$output = [];
while(true)
{
$row = mysqli_fetch_assoc($result);
if($row == null) break;
$output[] = $row;
}

echo(json_encode($output));