三表差异查询

Question

我有3个表：Names，ToDo，TasksDone。他们柱结构如下：

'Names' table: 
    Name (nvarchar) 
    Status (nvarchar) 

'ToDo' table: 
    Task (nvarchar) 
    Date (smalldatetime) 
    Name (nvarchar) 

'TasksDone' table: 
    TaskStatus (nvarchar) 
    Date (smalldatetime) 
    Name (nvarchar) 

'Names' table: 
Name | Status 
John | Available 
Ryan | Available 
Sean | NotAvailable 

'ToDo' table: 
Task  | Date  | Name 
Washing | 01.01.2012 | John 
Cleaning | 03.01.2012 | Ryan 
Washing | 04.01.2012 | Sean 

'TasksDone' table: 
TaskStatus| Date  | Name 
Done  | 01.01.2012 | John 
Done  | 02.01.2012 | Ryan 
NotDone | 02.01.2012 | Sean 

我想所有的Name从Names表Status='Available'未在指定天（日期）ToDo和TasksDone表中找到。

Answer 1

试试这个（YOUR_DATE是您的日期，必须更换）

SELECT 
    n.Name 
FROM Names n 
LEFT OUTER JOIN ToDo t 
    ON t.Name = n.Name 
    AND t.Date = YOUR_DATE 
LEFT OUTER JOIN TasksDone td 
    ON td.Name = n.Name 
    AND td.Date = YOUR_DATE 
WHERE 
    n.Status = 'Available' 
    AND t.Name IS NULL 
    AND td.Name IS NULL