SQL从Access中的两个不同表中减去值

Question

我有两个不同的表，每个表包含一个值。例如：

table1    table2 

|Hours_worked|  |Work_Completed| 
    250     346 

我想要我的查询从Work_completed中减去Hours_worked。我尝试这样做：

SELECT (SELECT Hours_worked FROM table1)- (SELECT Work_Completed FROM table2) AS Diff 

我得到的错误：“查询输入必须包含至少一个表或查询”

任何帮助将是巨大的，感谢

Answer 1

我觉得这纯粹是：

select Hours_worked - Work_Completed as diff 
from table1, table2 

Answer 2

只需添加FROM双，我的意思是：

SELECT 
(SELECT Hours_worked FROM table1) - (SELECT Work_Completed FROM table2) AS Diff 
FROM DUAL