第一个查询返回第二个查询的结果

在我的代码中，我正在检查db中是否存在一个值。如果存在，则返回错误。然而，如果没有……它应该在数据库中创建值。这是我的代码:

/**
 * Check if the string has been used before
 *
 * @return bool
 */
private function _checkStringBeenUsed ()
{
    echo "Running check!'n";
    if ($this->_sString === null) {
        parent::showErrorMessage('Invalid shared String', 1005);
    }
    $this->_validateString();
    $sSql     = "SELECT * FROM operator_string WHERE
                    operatorId = '{$this->_sOperator}' AND
                    sharedString = '{$this->_sString}' AND
                    time >= DATE_SUB(
                        NOW(),
                        INTERVAL 1 DAY
                    )";
    $rQur     = $this->_oDb->query($sSql);
    echo $sSql;
    echo "'n'n";
    echo "Rows: " . $rQur->num_rows;
    echo "'n'n";
    if ($rQur->num_rows > 0) {
        parent::showErrorMessage('Shared string already used', 1005);
    } else {
        $sSql = "INSERT INTO operator_string
                    (operatorId, sharedString, time, hash)
                    VALUES
                    ('{$this->_sOperator}',
                        '{$this->_sString}',
                        NOW(),
                        '{$this->_sHash}'
                    )";
        $this->_oDb->query($sSql);
    }
}
/**
 * Validates the string and the hash
 *
 * @return void
 */
private function _validateString ()
{
    $sHashString = $this->_sOperator . $this->_sSharedSecret . $this->_sString;
    $sHash = hash('sha256', $sHashString);
    if ($sHash != $this->_sHash) {
        parent::showErrorMessage('Invalid authentication hash send', 1006);
    }
}

这是我在iPhone上运行命令时的输出:

2013-03-27 21:43:08.560 MyApp[45315:c07] Result: Running check!
SELECT * FROM operator_string WHERE
                        operatorId = 'a8198231u82' AND
                        sharedString = 'cqCEYGIbNvF7HU1' AND
                        time >= DATE_SUB(
                            NOW(),
                            INTERVAL 1 DAY
                        )
Rows: 1
<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE error>
<error>
    <errorCode>1005</errorCode>
    <errorMessage>Shared string already used</errorMessage>
</error>

如果在调用运行之前表中没有数据，它怎么可能是1行?该方法只运行一次，插入操作完成之后执行选择操作。

编辑1
如果我注释掉Insert SQL行，它不会向DB添加任何内容。