我想检查product_id购物车表中是否存在以及是否存在定义变量$class = 'show'
这是我的代码：
$article = $db->query("
SELECT
b.price as price,
b.shop_id as shop_id,
c.image as image,
c.name as name,
a.id as id
FROM products AS a
INNER JOIN prices AS b ON a.ean = b.sku
INNER JOIN shops as c on b.shop_id = c.id
WHERE a.id = '$product_id'
");
while ($data = $article->fetch_object()) {
$price = $data->price;
$price2 = $data->price;
$price = number_format($price, 2, ',', '');
$shop_id = $data->shop_id;
$logo = $data->image;
$name = $data->name;
//some html code here
}
现在我不知道如何检查购物车表中是否存在该产品。在两个表中，uniqe是product_id
我会LEFT JOIN为此目的使用a （请注意本CASE WHEN .. THEN ..节）。它与购物车表联接，并且exists_in_cart如果购物车中存在产品，则选择一个名为1的列，否则选择0：
$article = $db->query("
SELECT
b.price as price,
b.shop_id as shop_id,
c.image as image,
c.name as name,
a.id as id,
CASE WHEN cart.product_id IS NULL THEN 0 ELSE 1 END as exists_in_cart
FROM products AS a
INNER JOIN prices AS b ON a.ean = b.sku
INNER JOIN shops as c on b.shop_id = c.id
LEFT JOIN cart on a.id = cart.product_id
WHERE a.id = '$product_id'
");
如果购物车中存在产品，则为1，否则为0：
$productInCart = $data->exists_in_cart == 1 ? TRUE : FALSE;
if ($productInCart) {
$class = 'show';
}
else {
// ...
}
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我来说两句