从mysql到mysqli更新代码[重复]

Question

我正在尝试更新旧脚本，如下所示。

mysql sql statement that works is:
$result = mysql_query( "SELECT products.products_id AS id, 
products_description.products_name AS name,
products.products_quantity AS quantity, products.products_weight AS weight, 
products.products_price AS price
FROM products, products_description WHERE 
products.products_id=products_description.products_id;") or 
die(mysql_error());

while($row = mysql_fetch_array( $result )) {

我无法工作的mysqli语句是：

$sql = "SELECT products_id, products_description.products_name, 
products_quantity, products_weight, products_price FROM products INNER JOIN 
products_description on products.products_id = 
products_description.products_id";

$result = mysqli_query($con, $sql);
if(mysqli_num_rows($result)>0){


while(null !== ($row = mysqli_fetch_assoc($result))) {

我收到的错误是：

Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean 
given in index.php on line 19

mysqli 语句有效，但在我将 products_description.products_name 添加到查询时无效。

Answer 1

mysqli_query() 返回：

对于成功的 SELECT、SHOW、DESCRIBE 或 EXPLAIN 查询，它将返回一个 mysqli_result 对象。

对于其他成功的查询，它将返回 TRUE。失败时为 FALSE

从您的错误中可以明显看出，您将False 设为$result，然后将其传入mysqli_num_rows()，预计为mysqli_result。

如果products 和products_description 两个表中存在相同的列名，则需要将$sql 修改如下，因为可能存在不明确的列错误。

$sql = "SELECT p.products_id, pd.products_name, p.products_quantity, p.products_weight, p.products_price 
FROM products p 
INNER JOIN products_description pd on p.products_id = pd.products_id";