如何使用单个SQL字符串从C＃中的多个表创建数据集？

Question

I'm new to C#, and I'm kinda clueless about how to use a single sql-string to retrieve data from multiple tables (3 of them, actually).

basically there are 2 master-files:

• Task_Information, Emp_Information

And 1 transaction-file:

• Assignments: this one gets updated by the primary keys of the 2 master-files and a few other fields.

And that's alright. But now i need to run a command that will retrieve data from ALL 3 tables based on a search-parameter entered by the user, and display selected fields in all of them. in ms access, all i had to do was make a query - here's the generated sql:

SELECT Assignments.Task_No, Assignments.Assignment_No, Assignments.Assignment_Date,
       Task_Information.Client_Name, Emp_Information.F_Name, Emp_Information.L_Name
  FROM Emp_Information 
       INNER JOIN (Task_Information 
                   INNER JOIN Assignments ON Task_Information.Task_No = Assignments.Task_No) 
             ON Emp_Information.Emp_ID = Assignments.Assignee
  WHERE (((Assignments.Assignment_Date)="this is just some date the user has to enter..."))

In short, I need to find out how to use the same sql-string in a C# program where the user types the search parameter and clicks a button. btw, it's got to be done with an oledbdatareader/adapter;

Answer 1

Try this query:

 SELECT Assignments.Task_No, Assignments.Assignment_No, Assignments.Assignment_Date,
 Task_Information.Client_Name, Emp_Information.F_Name, Emp_Information.L_Name
  FROM Emp_Information 
  INNER JOIN Task_Information 
  ON Task_Information.Task_No = Assignments.Task_No 
  INNER JOIN Assignments 
  ON Emp_Information.Emp_ID = Assignments.Assignee
  WHERE (((Assignments.Assignment_Date) like "%this is just some date the user has to enter...%"))

Answer 2

if you would work with an SQL Server you could use the SqlCommand . With this you would replace your string "this is..." with a parameter placeholder @date , which could then be set like shown on MSDN .

The main problem here would be the usage of the OleDbDataReader and if it supports this kind of query. But after reading the MSDN for OleDbCommand.Parameters it should work.