我無法弄清楚如何在SQL中使用$ where來選擇類別

Question

我想顯示從表中選擇的查詢

<?php 
    $where = "";

    if(isset($_GET['category']))
    {
        $catid = $_GET['category'];
        $where = " WHERE product.categoryid = $catid";
    }

因此，是獲取類別的$where函數

 $sql = "SELECT category.*,  
             category.category_id , items.id AS itemID,items.asset_tag,items.name,
                  items.brand,items.status,
                  items.quantity,items.category_id,
                items.color,items.texture,items.photo,items.date,
             items.fetch_item FROM items  LEFT JOIN category ON 
                     category.category_id=items.category_id 
                  WHERE  items.status = 'Available' AND items.fetch_item = '0' $where";


         ?>

Answer 1

看起來您犯了個小錯誤，因為在“默認”查詢中您已經有WHERE語句，因此在if中您應該再次使用AND或OR而不是WHERE ：

$where = "";
if(isset($_GET['category']))
{
    $catid=$_GET['category'];
    $where = " AND product.categoryid = $catid";
}

另外，通過使用sprintf（）函數，可以使注入其他WHERE條件更加優雅。 看一個例子：

$additional_condition = 'AND active=1'
$statement = 'SELECT * FROM users WHERE condition=1 %s';
echo sprintf($statement, $additional_condition);

// Output: SELECT * FROM users WHERE condition=1 AND active=1