SQL从Access

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

我希望我的查询从Work_completed中减去Hours_worked。我试过这个：

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

我收到错误：＆＃34;查询输入必须包含至少一个表或查询＆＃34;

任何帮助都会很棒，谢谢

Answer 1

我认为这只会是：

select Hours_worked - Work_Completed as diff
from table1, table2

Answer 2

只需添加FROM dual，我的意思是：

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