使用PHP双变量进入mysql查询时的不良行为

Question

我试图在mysql插入查询中使用不同的变量。我对所有字符串变量都没有问题，但是当我为NULL时，我无法实现工作的双变量。

$TemperatureMaxC = NULL;
if (array_key_exists('temperaturemaxc', $component_data))
{
    if ((string)$component_data["temperaturemaxc"] != '') {
        $TemperatureMaxC = "'".(string)$component_data["temperaturemaxc"]."'";
    }        
}
$TemperatureMaxC_cast = ($TemperatureMaxC == NULL ? NULL : $TemperatureMaxC);

$query = $this->db->query("INSERT INTO `Components`
                                        (`ManufacturerName`
                                        ,`ManufacturerPN`
                                        ,`IsDesignPart`
                                        ,`DesignPartID`
                                        ,`Published`
                                        ,`Author`
                                        ,`InternalStock`
                                        ,`LastModified`
                                        ,`TemperatureMaxC`)
                                VALUES
                                        (".$ManufacturerName."
                                       ,".$ManufacturerPN."
                                       ,1
                                       ,(SELECT `DesignPartID`
                                           FROM `DesignToManufacturingReference`
                                           WHERE (`Part Number` = ".$PartNumber." AND `Value1` = ".$Value1." AND `Value2` = ".$Value2." ))
                                       ,".$Published."
                                       ,".$Author."
                                       ,".$InternalStock."
                                       ,".$LastModified."
                                       ,".$TemperatureMaxC_cast."
                                       )");

我在$ TemperatureMaxC_cast为NULL时编写了不同的查询？

提前谢谢你：）