將表上的ID主鍵設置為另一個表作為外鍵

Question

我有三張桌子

表Customers ：

customerid    LastName    FirstName    Phone

表class ：

classid    numofstud    numofstud    totalprice

表Orderlist ：

orderid    customerid (FK_order_customer)    classid (FK_order_class])

我想將他們表中的最后一個customerid和classid設置為orderlist表。我使用身份增量。

SqlConnection con = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["miztahrirtest2DB"].ToString());
SqlCommand cmd = new SqlCommand("insert into customer (firstname,lastname,phone) values (@firstname,@lastname,@phone)", con);
cmd.Parameters.AddWithValue("firstname", firstnametxt.Text);
cmd.Parameters.AddWithValue("lastname", lastnametxt.Text);
cmd.Parameters.AddWithValue("phone", phonetxt.Text);
con.Open();
 cmd.ExecuteNonQuery();
con.Close();

SqlCommand cmd2 = new SqlCommand("insert into class (numofstud,numofclass,totalprice) values (@numofstud,@numofclass,@totalprice)", con);
cmd2.Parameters.AddWithValue("numofclass", Session["Numofclass"]);
cmd2.Parameters.AddWithValue("numofstud", Session["Numofstud"]);
cmd2.Parameters.AddWithValue("totalprice", Session["totalprice"]);
con.Open();
 cmd2.ExecuteNonQuery();
con.Close();

SqlCommand cmd3 = new SqlCommand("insert into orderlist (customerid,classid) values (SELECT MAX(customerid) FROM customer,SELECT MAX(classid) FROM class)", con);

con.Open();
cmd3.ExecuteNonQuery();
con.Close();

cmd和cmd2正常工作，但cmd3出現錯誤

ncorrect syntax near the keyword 'SELECT'.
Incorrect syntax near the keyword 'SELECT'.
Incorrect syntax near ')'.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.Data.SqlClient.SqlException: Incorrect syntax near the keyword 'SELECT'.
Incorrect syntax near the keyword 'SELECT'.
Incorrect syntax near ')'.

Source Error: 


Line 48:         con.Open();
Line 49:         cmd3.ExecuteNonQuery();
Line 50:         con.Close();
Line 51: 

Source File: c:\Users\Me.Groot\Documents\Visual Studio 2013\WebSites\miztahrirtest2\account.aspx.cs    Line: 49 

我現在應該怎么辦？

Answer 1

將您的cmd3命令文本更改為：

insert into orderlist (customerid,classid) SELECT MAX(customerid),MAX(classid) FROM customer, class

或者您可以使用SCOPE_IDENTITY()獲得最后的身份，因此您的代碼將是：

    SqlConnection con = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["miztahrirtest2DB"].ToString());
SqlCommand cmd = new SqlCommand("insert into customer (firstname,lastname,phone) values (@firstname,@lastname,@phone);SELECT SCOPE_IDENTITY()", con);
cmd.Parameters.AddWithValue("firstname", firstnametxt.Text);
cmd.Parameters.AddWithValue("lastname", lastnametxt.Text);
cmd.Parameters.AddWithValue("phone", phonetxt.Text);
con.Open();
 Int32 customerID = (Int32) cmd.ExecuteScalar();
con.Close();

SqlCommand cmd2 = new SqlCommand("insert into class (numofstud,numofclass,totalprice) values (@numofstud,@numofclass,@totalprice);SELECT SCOPE_IDENTITY()", con);
cmd2.Parameters.AddWithValue("numofclass", Session["Numofclass"]);
cmd2.Parameters.AddWithValue("numofstud", Session["Numofstud"]);
cmd2.Parameters.AddWithValue("totalprice", Session["totalprice"]);
con.Open();
 Int32 classID = (Int32) cmd2.ExecuteScalar();
con.Close();

SqlCommand cmd3 = new SqlCommand("insert into orderlist (customerid,classid) values (@customerId,@classId)", con);
cmd3.Parameters.AddWithValue("customerId", customerID );
cmd3.Parameters.AddWithValue("classId",classID );

con.Open();
cmd3.ExecuteNonQuery();
con.Close();

Answer 2

您的select語句不正確，請嘗試以下操作：

SELECT
    MAX(cust.customerid),
    MAX(cls.classid)
FROM customer cust, class cls

Answer 3

要從表中獲取last value ，可以使用last()函數

SELECT LAST(column_name) FROM table_name