[英]how to sum two columns from different tables
$username = mysqli_real_escape_string($con, $_SESSION['username']);
$qry="(SELECT SUM(amount) from deposits) + (SELECT SUM(amount) from referral) as value_sum WHERE username ='$username' ";
我曾嘗試使用它,但我不斷收到此錯誤。
您的 SQL 語法有錯誤; 檢查與您的 MariaDB 服務器版本相對應的手冊以獲取正確的語法,以在第 1 行使用近 '+ (SELECT SUM(amount) fromreferral) as value_sum WHERE username ='test0''
您創建兩個查詢並使用 UNION 將結果彼此相加:
SELECT SUM(value_sum)
FROM (
SELECT SUM(amount) as value_sum
FROM deposits AS D
WHERE username = '$username'
UNION
SELECT SUM(amount) as value_sum
FROM referral AS R
WHERE username = '$username'
) AS U
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