当查询返回零行时，查询和while循环不能正确工作 - query and while loop don't work correctly when query returns zero rows

我的查询和while循环解析行正确工作时，行数> 0，但不=0时。

当返回的行数为0时，似乎跳过了整个while循环。请参阅$activeCount强制=0的注释，并且不会执行并出现以下错误消息。

在下面的代码之前，在数组$errorMessages[]中设置了一个默认的错误消息，并在触发器发生时更新和添加它。当查询中返回0行时，不会对$ error_noactivities进行更新。

相关代码

//fetch the user's active posts and their count
$fetch = mysql_query("SELECT SQL_CALC_FOUND_ROWS * FROM (
    SELECT propertyID, streetAddress, city3, city2 FROM residence.property
    INNER JOIN contact ON residence.contact.ContactID = residence.property.ContactID
    WHERE residence.contact.contactEmailAddress1 ='$contactEmailAddress1' AND activePosting = '1') props,
    (SELECT FOUND_ROWS() AS 'activeCount') actives;")
    or die('<li class=error>Ooops</li>'. mysql_error());
//create HTML li items to show each posting and create jQuery to insert to a div
$rowCount = 0;
while ($row = mysql_fetch_array($fetch)) {
    $activeCount = $row["activeCount"];
    //$activeCount = 0; //test - get default error message, seems next 3+ lines are not executing when query has 0 rows
    if( $activeCount == 0 ) {
    $error_NoActives = "<li>You have $activeCount active postings.</li>";
    //don't get this message with 0 active posts, get default error
    $errorMessages[0] = $error_NoActives;
    } else {
        //$activeCount displays correctly if non-zero
        $error_NumberOfActives = "<ul>Welcome back. You have $activeCount active postings.
        //do stuff using $rowCount. Construct li items.
        $rowCount++;
        }
    }
}

我怀疑我不理解一些关于while循环，或关于MySQL的FOUND_ROWS()和SQL_CALC_FOUND_ROWS。

无论如何，当查询返回0行时，$ error_noactivities语句不会执行。

while循环只会在有结果的情况下运行。这是正常运行的，因为如果它试图运行没有结果，那么$row中的所有值都将为空。

正确的方法是这样使用mysql_num_rows:

if(mysql_num_rows($fetch)) {
    while($row = mysql_fetch_assoc($fetch)) {
        $error_NumberOfActives = "<ul>Welcome back. You have $activeCount active postings.
        //Do stuff with $row.
    }
} else {
    $error_NoActives = "<li>You have $activeCount active postings.</li>";
}

你可以完全从你的查询中删除SELECT FOUND_ROWS()。

另外，另一个值得注意的点是你的die语句。如果你只是在测试时使用它，那么它是可以的。但是不要依赖于运行代码的死亡语句。一个更好的解决方案是:

$query = "mysqlquery";
if(mysql_query($query)) {
} else {
    //some error code
}

这样可以更好地处理错误

while循环不运行，因为没有什么可循环的，因为您有0行。如果有超过0行，则在WHILE周围设置if语句，如果有0行，则在else中可以使用代码。还修复了欢迎信息中的语法错误。

//fetch the user's active posts and their count
$fetch = mysql_query("SELECT SQL_CALC_FOUND_ROWS * FROM (
    SELECT propertyID, streetAddress, city3, city2 FROM residence.property
    INNER JOIN contact ON residence.contact.ContactID = residence.property.ContactID
    WHERE residence.contact.contactEmailAddress1 ='$contactEmailAddress1' AND activePosting = '1') props,
    (SELECT FOUND_ROWS() AS 'activeCount') actives;")
    or die('<li class=error>Ooops</li>'. mysql_error());
//create HTML li items to show each posting and create jQuery to insert to a div
$rowCount = 0;
if( mysql_num_rows($fetch) > 0 )
{
    while ($row = mysql_fetch_array($fetch)) {
        $activeCount = $row["activeCount"];
        //$activeCount = 0; //test - get default error message, seems next 3+ lines are not executing when query has 0 rows
            //$activeCount displays correctly if non-zero
            $error_NumberOfActives = "<ul>Welcome back. You have $activeCount active postings.";
            //do stuff using $rowCount. Construct li items.
            $rowCount++;
            }
    }
}
else {
    $error_NoActives = "<li>You have $activeCount active postings.</li>";
    //don't get this message with 0 active posts, get default error
    $errorMessages[0] = $error_NoActives;
}