将表中的 id 主键设置为另一个表作为外键

Question

我有三张桌子

表Customers:

customerid    LastName    FirstName    Phone

表class：

classid    numofstud    numofstud    totalprice

表Orderlist：

orderid    customerid (FK_order_customer)    classid (FK_order_class])

我想将他们表中的最后一个 customerid 和 classid 设置到 orderlist 表中。我为他们使用标识增量。

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 工作正常，但 cmd3 出现错误

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 

我现在该怎么办？

Answer 1

将您的 cmd3 命令文本更改为：

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

或者您可以使用SCOPE_IDENTITY() 获取最后一个身份，这样您的代码将是：

    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 语句不正确，试试这个：

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

Answer 3

要从表中获取last value，您可以使用last() 函数

SELECT LAST(column_name) FROM table_name