为什么空减空输出是0?
有一个表uuu,只有1条数据,如下:
<br />$aaa = false;<br />查询语句:'select * from uuu where id='.$aaa<br />
执行这条查询返回的是false,还是' ',还是null,还是什么啊?
我试了这个:
<br />$k = '' - '';<br />$k = null - null;<br />echo $k;<br />
输出的都是0

------解决思路----------------------
$aaa=false;
$sql = 'select * from uuu where id='.$aaa;
var_dump($sql);
false 连接于字符串的时候 为空字符串
输出为string(27) "select * from uuu where id="
上面的SQL mysql 语法检测不通过 所以给你返回了false 表示查询失败
------解决思路----------------------
要看变量值,不要用echo,要用var_dump
------解决思路----------------------
您的查询指令返回空记录,所以无所谓 是false,还是' ',还是null
当记录集不为空,且字段值为 null 时,除 PDO 可以指定外,其他数据库函数都返回 ‘’(空字符串)
------解决思路----------------------
$aaa = false;
查询语句:'select * from uuu where id='.$aaa
返回空紀錄,因為沒有匹配id=false的紀錄。
$k = '' - '';
$k = null - null;
var_dump($k);

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