如何只回显 php foreach 循环结果的一条消息，如果没有结果则隐藏该消息

Question

嗨，我正在尝试显示 php foreach 循环结果的常见消息。该消息必须在结果之前显示，如果没有结果，则不应显示。

<!-- An array coming from the previous page -->
$string = explode(PHP_EOL, trim($_SESSION['grid']));
<!-- HIDE THIS MESSAGE IF THERE ARE NO RESULTS --> 
<label>These barcodes don't exist:</label>   
foreach ($string as $value) {
    <!-- SQL QUERY -->
    $query1 = "select addl_item_code_barcode from items where 
    addl_item_code_barcode = '$value';";
    $result = pg_query($db, $query1);
    <!-- IF THE VALUES IN THE ARRAY DON'T EXIST IN THE DATABASE THEN IT IS TO 
    BE DISPLAYED -->
    if (pg_num_rows($result) == 0) {
        echo $value; echo' ';
    } 
}

问题是多个值不会显示在循环之外，并且结果不会在循环之前显示。我该如何解决这个问题？

Answer 1

不要立即回显输出，而是将其存储在字符串变量中，然后在标签之后输出

<?php
// An array coming from the previous page
$string = explode(PHP_EOL, trim($_SESSION['grid']));
$values = "";
foreach ($string as $value) {
    <!-- SQL QUERY -->
    $query1 = "
        SELECT addl_item_code_barcode 
          FROM items 
         WHERE addl_item_code_barcode = '$value'
             ;
    ";
    $result = pg_query($db, $query1);
    // IF THE VALUES IN THE ARRAY DON'T EXIST IN THE DATABASE THEN IT IS TO BE DISPLAYED
    if (pg_num_rows($result) == 0) {
        $values .= "{$value} ";
    } 
}
if (strlen($values) === 0) {
    // HIDE THIS MESSAGE IF THERE ARE NO RESULTS
    ?><label>These barcodes don't exist:</label><?php
}

Answer 2

$nonexistent = array();
foreach ($string as $value) {
$query1 = "select addl_item_code_barcode from items where 
addl_item_code_barcode = '$value';";
$result = pg_query($db, $query1);

if (pg_num_rows($result) == 0) {
array_push($nonexistent,$value);
        } 
}
if(count($nonexistent)>0){
    echo "<label>These barcodes don't exist:</label> <br/>";
    foreach($nonexistent as $element){
        echo $element . "<br/>";
    }
}