php - 如果表mysqli中的同一列，如何计算行x和行y

Question

如何计算第 1 行和第 4 行同一列。

我的代码:

$qR1 = mysqli_query($con, "SELECT * FROM tbproduct WHERE nameproduct = '".$product."'");
while( $res1 = mysqli_fetch_assoc($qR1)){
    $qR2 = mysqli_query($con, "SELECT * FROM tbvalproduct WHERE nameproduct = '".$res1['product']."' ");
    while($res2 = mysqli_fetch_assoc($qR2)){
        echo $res2['product']."=".$res2['value']."<br>";
    }

}

输出:

1.product1 = 1500000
2.product1 = 1400000
3.product1 = 1300000
4.product2 = 1000000
5.product2 = 900000
6.product2 = 800000

我想要的:

-row 1 + row 4 // 1500000 + 1000000
-row 2 + row 5 // 1400000 + 900000
-row 3 + row 6 // 1300000 + 800000

示例表:

Id      product       value
---------------------------    
1    product1       1500000
2    product1       1400000
3    product1        1300000
4    product2        1000000
5    product2         900000
6    product2         800000

Answer 1

您只需一个查询就可以做到这一点:

SELECT t1.product, t1.value
FROM tbvalproduct t1
INNER JOIN tbproduct t2
    ON t1.nameproduct = t2.product
WHERE
    t2.nameproduct = ?;

您更新的 PHP 代码:

$sql = "SELECT t1.product, t1.value FROM tbvalproduct t1 INNER JOIN tbproduct t2 ";
$sql .= "ON t1.nameproduct = t2.product WHERE t2.nameproduct = ?";

if ($stmt = $mysqli->prepare($sql)) {
    $stmt->bind_param("s", $product);
    $stmt->execute();
    $result = $stmt->get_result();

    while ($row = $result->fetch_assoc()) {

        echo $row['product']."=".$row['value']."<br>";
    }

   $stmt->free_result();
   $stmt->close();
}