sql減去子查詢總和多個表

Question

如何從另一個表中減去子查詢表的總和？

SELECT i.column1 * i.column2 AS Expr1 
    , i.column1 * i.column2 - (SELECT SUM(table2.column1) AS Expr1 
           FROM table2 
           WHERE (table2.column3 = table1.column3)) AS derivedExpression 
FROM table1 

只有第一行中的derivedExpression是正確的。其餘行爲derivedExpression返回null。對於Expr1，一切都很好。任何幫助？

Answer 1

SELECT i.column1 * i.column2 AS Expr1 
    , i.column1 * i.column2 - (SELECT COALESCE(SUM(table2.column1), 0) AS Expr1 
           FROM table2 
           WHERE (table2.column3 = table1.column3)) AS derivedExpression 
FROM table1