Php 带有NOTNULL变量的where子句

下面的一些变量（us1或sp1..）可能有空值（客户有可能不填写相应的文本视图）。如何将“where”子句的语法设置为仅包含“notnull”变量；例如，当us1不为null且sp1为null时，“where”子句必须为：“where customer.username1='us1'” 提前谢谢

$us1 = $_POST['username1'];
$sp1 = $_POST['startPoli1'];

SELECT `username1`,`startPoli1`, `finalPoli1`,`weight1` ,`phone1` 
 FROM customer ,registration1 
 where  customer.startPoli1 = 'sp1' and customer.username1 = 'us1'

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以这种方式写入条件：

WHERE ('sp1' IS NULL OR customer.startPoli1 = 'sp1')
AND ('us1' IS NULL OR customer.username1 = 'us1')

像这样：

$us1 = $_POST['username1'];
$sp1 = $_POST['startPoli1'];

$sql = "SELECT `username1`,`startPoli1`, `finalPoli1`,`weight1` ,`phone1` 
 FROM customer ,registration1 where 1=1 ";

if($sp1 != null)
   $sql += "and customer.startPoli1 = 'sp1'";
if($us1 != null) 
   $sql += "and customer.username1 = 'us1'";

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我认为，这是一个值得商榷的错误。忘记了$sp1和$us1是变量

$us1 = $_POST['username1'];
$sp1 = $_POST['startPoli1'];

$sql = "SELECT `username1`,`startPoli1`, `finalPoli1`,`weight1` ,`phone1` 
 FROM customer ,registration1 where 1=1 ";

if($sp1 != null)
   $sql += "and customer.startPoli1 = '" + $sp1 + "'";
if($us1 != null) 
   $sql += "and customer.username1 = '" + $us1 + "'";

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使用

if

并动态生成查询。在查询中可能重复使用nvl？可能重复