.NET Framework Class Library
SqlCommand Class

Represents a Transact-SQL statement or stored procedure to execute against a SQL Server database. This class cannot be inherited.

Namespace:   System.Data.SqlClient
Assembly:  System.Data (in System.Data.dll)
Syntax
Public NotInheritable Class SqlCommand _
	Inherits [%$TOPIC/z4956bkc_en-us_VS_110_2_0_0_0_0%] _
	Implements [%$TOPIC/z4956bkc_en-us_VS_110_2_0_0_0_1%]
public sealed class SqlCommand : [%$TOPIC/z4956bkc_en-us_VS_110_2_0_1_0_0%], 
	[%$TOPIC/z4956bkc_en-us_VS_110_2_0_1_0_1%]
public ref class SqlCommand sealed : public [%$TOPIC/z4956bkc_en-us_VS_110_2_0_2_0_0%], 
	[%$TOPIC/z4956bkc_en-us_VS_110_2_0_2_0_1%]
[<[%$TOPIC/z4956bkc_en-us_VS_110_2_0_3_0_0%]>]
type SqlCommand =  
    class 
        inherit [%$TOPIC/z4956bkc_en-us_VS_110_2_0_3_0_1%] 
        interface [%$TOPIC/z4956bkc_en-us_VS_110_2_0_3_0_2%] 
    end

The SqlCommand type exposes the following members.

Constructors
  NameDescription
Public method SqlCommandInitializes a new instance of the SqlCommand class.
Public method SqlCommand(String)Initializes a new instance of the SqlCommand class with the text of the query.
Public method SqlCommand(String, SqlConnection)Initializes a new instance of the SqlCommand class with the text of the query and a SqlConnection.
Public method SqlCommand(String, SqlConnection, SqlTransaction)Initializes a new instance of the SqlCommand class with the text of the query, a SqlConnection, and the SqlTransaction.
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Properties
  NameDescription
Public property CommandTextGets or sets the Transact-SQL statement, table name or stored procedure to execute at the data source. (Overrides DbCommandCommandText.)
Public property CommandTimeoutGets or sets the wait time before terminating the attempt to execute a command and generating an error. (Overrides DbCommandCommandTimeout.)
Public property CommandTypeGets or sets a value indicating how the CommandText property is to be interpreted. (Overrides DbCommandCommandType.)
Public property ConnectionGets or sets the SqlConnection used by this instance of the SqlCommand.
Public property ContainerGets the IContainer that contains the Component. (Inherited from Component.)
Public property DesignTimeVisibleGets or sets a value indicating whether the command object should be visible in a Windows Form Designer control. (Overrides DbCommandDesignTimeVisible.)
Public property NotificationGets or sets a value that specifies the SqlNotificationRequest object bound to this command.
Public property NotificationAutoEnlistGets or sets a value indicating whether the application should automatically receive query notifications from a common SqlDependency object.
Public property ParametersGets the SqlParameterCollection.
Public property SiteGets or sets the ISite of the Component. (Inherited from Component.)
Public property TransactionGets or sets the SqlTransaction within which the SqlCommand executes.
Public property UpdatedRowSourceGets or sets how command results are applied to the DataRow when used by the Update method of the DbDataAdapter. (Overrides DbCommandUpdatedRowSource.)
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Methods
  NameDescription
Public method BeginExecuteNonQueryInitiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand.
Public method BeginExecuteNonQuery(AsyncCallback, Object)Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand, given a callback procedure and state information.
Public method BeginExecuteReaderInitiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand, and retrieves one or more result sets from the server.
Public method BeginExecuteReader(CommandBehavior)Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand using one of the CommandBehavior values.
Public method BeginExecuteReader(AsyncCallback, Object)Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand and retrieves one or more result sets from the server, given a callback procedure and state information.
Public method BeginExecuteReader(AsyncCallback, Object, CommandBehavior)Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand, using one of the CommandBehavior values, and retrieving one or more result sets from the server, given a callback procedure and state information.
Public method BeginExecuteXmlReaderInitiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand and returns results as an XmlReader object.
Public method BeginExecuteXmlReader(AsyncCallback, Object)Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand and returns results as an XmlReader object, using a callback procedure.
Public method CancelTries to cancel the execution of a SqlCommand. (Overrides DbCommandCancel.)
Public method CloneCreates a new SqlCommand object that is a copy of the current instance.
Public method CreateObjRefCreates an object that contains all the relevant information required to generate a proxy used to communicate with a remote object. (Inherited from MarshalByRefObject.)
Public method CreateParameterCreates a new instance of a SqlParameter object.
Public method DisposeReleases all resources used by the Component. (Inherited from Component.)
Public method EndExecuteNonQueryFinishes asynchronous execution of a Transact-SQL statement.
Public method EndExecuteReaderFinishes asynchronous execution of a Transact-SQL statement, returning the requested SqlDataReader.
Public method EndExecuteXmlReaderFinishes asynchronous execution of a Transact-SQL statement, returning the requested data as XML.
Public method Equals(Object)Determines whether the specified object is equal to the current object. (Inherited from Object.)
Public method ExecuteNonQueryExecutes a Transact-SQL statement against the connection and returns the number of rows affected. (Overrides DbCommandExecuteNonQuery.)
Public method ExecuteNonQueryAsyncAn asynchronous version of ExecuteNonQuery, which executes a SQL statement against a connection object.Invokes ExecuteNonQueryAsync with CancellationToken.None. (Inherited from DbCommand.)
Public method ExecuteNonQueryAsync(CancellationToken)An asynchronous version of ExecuteNonQuery, which executes a Transact-SQL statement against the connection and returns the number of rows affected. The cancellation token can be used to request that the operation be abandoned before the command timeout elapses. Exceptions will be reported via the returned Task object. (Overrides DbCommandExecuteNonQueryAsync(CancellationToken).)
Public method ExecuteReaderSends the CommandText to the Connection and builds a SqlDataReader.
Public method ExecuteReader(CommandBehavior)Sends the CommandText to the Connection, and builds a SqlDataReader using one of the CommandBehavior values.
Public method ExecuteReaderAsyncAn asynchronous version of ExecuteReader, which sends the CommandText to the Connection and builds a SqlDataReader. Exceptions will be reported via the returned Task object.
Public method ExecuteReaderAsync(CancellationToken)An asynchronous version of ExecuteReader, which sends the CommandText to the Connection and builds a SqlDataReader.The cancellation token can be used to request that the operation be abandoned before the command timeout elapses. Exceptions will be reported via the returned Task object.
Public method ExecuteReaderAsync(CommandBehavior)An asynchronous version of ExecuteReader, which sends the CommandText to the Connection, and builds a SqlDataReader. Exceptions will be reported via the returned Task object.
Public method ExecuteReaderAsync(CommandBehavior, CancellationToken)An asynchronous version of ExecuteReader, which sends the CommandText to the Connection, and builds a SqlDataReaderThe cancellation token can be used to request that the operation be abandoned before the command timeout elapses. Exceptions will be reported via the returned Task object.
Public method ExecuteScalarExecutes the query, and returns the first column of the first row in the result set returned by the query. Additional columns or rows are ignored. (Overrides DbCommandExecuteScalar.)
Public method ExecuteScalarAsyncAn asynchronous version of ExecuteScalar, which executes the query and returns the first column of the first row in the result set returned by the query. All other columns and rows are ignored.Invokes ExecuteScalarAsync with CancellationToken.None. (Inherited from DbCommand.)
Public method ExecuteScalarAsync(CancellationToken)An asynchronous version of ExecuteScalar, which executes the query asynchronously and returns the first column of the first row in the result set returned by the query. Additional columns or rows are ignored.The cancellation token can be used to request that the operation be abandoned before the command timeout elapses. Exceptions will be reported via the returned Task object. (Overrides DbCommandExecuteScalarAsync(CancellationToken).)
Public method ExecuteXmlReaderSends the CommandText to the Connection and builds an XmlReader object.
Public method ExecuteXmlReaderAsyncAn asynchronous version of ExecuteXmlReader, which sends the CommandText to the Connection and builds an XmlReader object.Exceptions will be reported via the returned Task object.
Public method ExecuteXmlReaderAsync(CancellationToken)An asynchronous version of ExecuteXmlReader, which sends the CommandText to the Connection and builds an XmlReader object.The cancellation token can be used to request that the operation be abandoned before the command timeout elapses. Exceptions will be reported via the returned Task object.
Public method GetHashCodeServes as the default hash function. (Inherited from Object.)
Public method GetLifetimeServiceRetrieves the current lifetime service object that controls the lifetime policy for this instance. (Inherited from MarshalByRefObject.)
Public method GetTypeGets the Type of the current instance. (Inherited from Object.)
Public method InitializeLifetimeServiceObtains a lifetime service object to control the lifetime policy for this instance. (Inherited from MarshalByRefObject.)
Public method PrepareCreates a prepared version of the command on an instance of SQL Server. (Overrides DbCommandPrepare.)
Public method ResetCommandTimeoutResets the CommandTimeout property to its default value.
Public method ToStringReturns a String containing the name of the Component, if any. This method should not be overridden. (Inherited from Component.)
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Events
  NameDescription
Public event DisposedOccurs when the component is disposed by a call to the Dispose method. (Inherited from Component.)
Public event StatementCompletedOccurs when the execution of a Transact-SQL statement completes.
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Explicit Interface Implementations
  NameDescription
Explicit interface implemetation Private method ICloneableCloneCreates a new SqlCommand object that is a copy of the current instance.
Explicit interface implemetation Private property IDbCommandConnectionGets or sets the IDbConnection used by this instance of the IDbCommand. (Inherited from DbCommand.)
Explicit interface implemetation Private method IDbCommandCreateParameterCreates a new instance of an IDbDataParameter object. (Inherited from DbCommand.)
Explicit interface implemetation Private method IDbCommandExecuteReaderExecutes the CommandText against the Connection and builds an IDataReader. (Inherited from DbCommand.)
Explicit interface implemetation Private method IDbCommandExecuteReader(CommandBehavior)Executes the CommandText against the Connection, and builds an IDataReader using one of the CommandBehavior values. (Inherited from DbCommand.)
Explicit interface implemetation Private property IDbCommandParametersGets the IDataParameterCollection. (Inherited from DbCommand.)
Explicit interface implemetation Private property IDbCommandTransactionGets or sets the DbTransaction within which this DbCommand object executes. (Inherited from DbCommand.)
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Remarks

When an instance of SqlCommand is created, the read/write properties are set to their initial values. For a list of these values, see the SqlCommand constructor.

SqlCommand features the following methods for executing commands at a SQL Server database:

Item

Description

BeginExecuteNonQuery

Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand, generally executing commands such as INSERT, DELETE, UPDATE, and SET statements. Each call to BeginExecuteNonQuery must be paired with a call to EndExecuteNonQuery which finishes the operation, typically on a separate thread.

BeginExecuteReader

Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand and retrieves one or more results sets from the server. Each call to BeginExecuteReader must be paired with a call to EndExecuteReader which finishes the operation, typically on a separate thread.

BeginExecuteXmlReader

Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand. Each call to BeginExecuteXmlReader must be paired with a call to EndExecuteXmlReader, which finishes the operation, typically on a separate thread, and returns an XmlReader object.

ExecuteReader

Executes commands that return rows. For increased performance, ExecuteReader invokes commands using the Transact-SQL sp_executesql system stored procedure. Therefore, ExecuteReader might not have the effect that you want if used to execute commands such as Transact-SQL SET statements.

ExecuteNonQuery

Executes commands such as Transact-SQL INSERT, DELETE, UPDATE, and SET statements.

ExecuteScalar

Retrieves a single value (for example, an aggregate value) from a database.

ExecuteXmlReader

Sends the CommandText to the Connection and builds an XmlReader object.

You can reset the CommandText property and reuse the SqlCommand object. However, you must close the SqlDataReader before you can execute a new or previous command.

If a SqlException is generated by the method executing a SqlCommand, the SqlConnection remains open when the severity level is 19 or less. When the severity level is 20 or greater, the server ordinarily closes the SqlConnection. However, the user can reopen the connection and continue.

NoteNote

Nameless, also called ordinal, parameters are not supported by the .NET Framework Data Provider for SQL Server.

Examples

The following example creates a SqlConnection, a SqlCommand, and a SqlDataReader. The example reads through the data, writing it to the console. Finally, the example closes the SqlDataReader and then the SqlConnection as it exits the Using code blocks.

Public Sub ReadOrderData(ByVal connectionString As String)
    Dim queryString As String = _
        "SELECT OrderID, CustomerID FROM dbo.Orders;" 
    Using connection As New SqlConnection(connectionString)
        Dim command As New SqlCommand(queryString, connection)
        connection.Open()
        Dim reader As SqlDataReader = command.ExecuteReader()
        Try 
            While reader.Read()
                Console.WriteLine(String.Format("{0}, {1}", _
                    reader(0), reader(1)))
            End While 
        Finally 
            ' Always call Close when done reading.
            reader.Close()
        End Try 
    End Using 
End Sub
private static void ReadOrderData(string connectionString)
{
    string queryString = 
        "SELECT OrderID, CustomerID FROM dbo.Orders;";
    using (SqlConnection connection = new SqlConnection(
               connectionString))
    {
        SqlCommand command = new SqlCommand(
            queryString, connection);
        connection.Open();
        SqlDataReader reader = command.ExecuteReader();
        try
        {
            while (reader.Read())
            {
                Console.WriteLine(String.Format("{0}, {1}",
                    reader[0], reader[1]));
            }
        }
        finally
        {
            // Always call Close when done reading.
            reader.Close();
        }
    }
}

The following sample shows how to create and execute different types of SqlCommand objects.

First you must create the sample database, by executing the following script:

USE [master]
GO

CREATE DATABASE [MySchool]
GO

USE [MySchool]
GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE procedure [dbo].[CourseExtInfo] @CourseId int
as
select c.CourseID,c.Title,c.Credits,d.Name as DepartmentName
from Course as c left outer join Department as d on c.DepartmentID=d.DepartmentID
where c.CourseID=@CourseId

GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
create procedure [dbo].[DepartmentInfo] @DepartmentId int,@CourseCount int output
as
select @CourseCount=Count(c.CourseID)
from course as c
where c.DepartmentID=@DepartmentId

select d.DepartmentID,d.Name,d.Budget,d.StartDate,d.Administrator
from Department as d
where d.DepartmentID=@DepartmentId

GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
Create PROCEDURE [dbo].[GetDepartmentsOfSpecifiedYear] 
@Year int,@BudgetSum money output
AS
BEGIN
        SELECT @BudgetSum=SUM([Budget])
  FROM [MySchool].[dbo].[Department]
  Where YEAR([StartDate])=@Year 

SELECT [DepartmentID]
      ,[Name]
      ,[Budget]
      ,[StartDate]
      ,[Administrator]
  FROM [MySchool].[dbo].[Department]
  Where YEAR([StartDate])=@Year

END
GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Course](
[CourseID] [nvarchar](10) NOT NULL,
[Year] [smallint] NOT NULL,
[Title] [nvarchar](100) NOT NULL,
[Credits] [int] NOT NULL,
[DepartmentID] [int] NOT NULL,
 CONSTRAINT [PK_Course] PRIMARY KEY CLUSTERED 
(
[CourseID] ASC,
[Year] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Department](
[DepartmentID] [int] IDENTITY(1,1) NOT NULL,
[Name] [nvarchar](50) NOT NULL,
[Budget] [money] NOT NULL,
[StartDate] [datetime] NOT NULL,
[Administrator] [int] NULL,
 CONSTRAINT [PK_Department] PRIMARY KEY CLUSTERED 
(
[DepartmentID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Person](
[PersonID] [int] IDENTITY(1,1) NOT NULL,
[LastName] [nvarchar](50) NOT NULL,
[FirstName] [nvarchar](50) NOT NULL,
[HireDate] [datetime] NULL,
[EnrollmentDate] [datetime] NULL,
 CONSTRAINT [PK_School.Student] PRIMARY KEY CLUSTERED 
(
[PersonID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[StudentGrade](
[EnrollmentID] [int] IDENTITY(1,1) NOT NULL,
[CourseID] [nvarchar](10) NOT NULL,
[StudentID] [int] NOT NULL,
[Grade] [decimal](3, 2) NOT NULL,
 CONSTRAINT [PK_StudentGrade] PRIMARY KEY CLUSTERED 
(
[EnrollmentID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
create view [dbo].[EnglishCourse]
as
select c.CourseID,c.Title,c.Credits,c.DepartmentID
from Course as c join Department as d on c.DepartmentID=d.DepartmentID
where d.Name=N'English'

GO
INSERT [dbo].[Course] ([CourseID], [Year], [Title], [Credits], [DepartmentID]) VALUES (N'C1045', 2012, N'Calculus', 4, 7)
INSERT [dbo].[Course] ([CourseID], [Year], [Title], [Credits], [DepartmentID]) VALUES (N'C1061', 2012, N'Physics', 4, 1)
INSERT [dbo].[Course] ([CourseID], [Year], [Title], [Credits], [DepartmentID]) VALUES (N'C2021', 2012, N'Composition', 3, 2)
INSERT [dbo].[Course] ([CourseID], [Year], [Title], [Credits], [DepartmentID]) VALUES (N'C2042', 2012, N'Literature', 4, 2)
SET IDENTITY_INSERT [dbo].[Department] ON 

INSERT [dbo].[Department] ([DepartmentID], [Name], [Budget], [StartDate], [Administrator]) VALUES (1, N'Engineering', 350000.0000, CAST(0x0000999C00000000 AS DateTime), 2)
INSERT [dbo].[Department] ([DepartmentID], [Name], [Budget], [StartDate], [Administrator]) VALUES (2, N'English', 120000.0000, CAST(0x0000999C00000000 AS DateTime), 6)
INSERT [dbo].[Department] ([DepartmentID], [Name], [Budget], [StartDate], [Administrator]) VALUES (4, N'Economics', 200000.0000, CAST(0x0000999C00000000 AS DateTime), 4)
INSERT [dbo].[Department] ([DepartmentID], [Name], [Budget], [StartDate], [Administrator]) VALUES (7, N'Mathematics', 250024.0000, CAST(0x0000999C00000000 AS DateTime), 3)
SET IDENTITY_INSERT [dbo].[Department] OFF
SET IDENTITY_INSERT [dbo].[Person] ON 

INSERT [dbo].[Person] ([PersonID], [LastName], [FirstName], [HireDate], [EnrollmentDate]) VALUES (1, N'Hu', N'Nan', NULL, CAST(0x0000A0BF00000000 AS DateTime))
INSERT [dbo].[Person] ([PersonID], [LastName], [FirstName], [HireDate], [EnrollmentDate]) VALUES (2, N'Norman', N'Laura', NULL, CAST(0x0000A0BF00000000 AS DateTime))
INSERT [dbo].[Person] ([PersonID], [LastName], [FirstName], [HireDate], [EnrollmentDate]) VALUES (3, N'Olivotto', N'Nino', NULL, CAST(0x0000A0BF00000000 AS DateTime))
INSERT [dbo].[Person] ([PersonID], [LastName], [FirstName], [HireDate], [EnrollmentDate]) VALUES (4, N'Anand', N'Arturo', NULL, CAST(0x0000A0BF00000000 AS DateTime))
INSERT [dbo].[Person] ([PersonID], [LastName], [FirstName], [HireDate], [EnrollmentDate]) VALUES (5, N'Jai', N'Damien', NULL, CAST(0x0000A0BF00000000 AS DateTime))
INSERT [dbo].[Person] ([PersonID], [LastName], [FirstName], [HireDate], [EnrollmentDate]) VALUES (6, N'Holt', N'Roger', CAST(0x000097F100000000 AS DateTime), NULL)
INSERT [dbo].[Person] ([PersonID], [LastName], [FirstName], [HireDate], [EnrollmentDate]) VALUES (7, N'Martin', N'Randall', CAST(0x00008B1A00000000 AS DateTime), NULL)
SET IDENTITY_INSERT [dbo].[Person] OFF
SET IDENTITY_INSERT [dbo].[StudentGrade] ON 

INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (1, N'C1045', 1, CAST(3.50 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (2, N'C1045', 2, CAST(3.00 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (3, N'C1045', 3, CAST(2.50 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (4, N'C1045', 4, CAST(4.00 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (5, N'C1045', 5, CAST(3.50 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (6, N'C1061', 1, CAST(4.00 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (7, N'C1061', 3, CAST(3.50 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (8, N'C1061', 4, CAST(2.50 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (9, N'C1061', 5, CAST(1.50 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (10, N'C2021', 1, CAST(2.50 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (11, N'C2021', 2, CAST(3.50 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (12, N'C2021', 4, CAST(3.00 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (13, N'C2021', 5, CAST(3.00 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (14, N'C2042', 1, CAST(2.00 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (15, N'C2042', 2, CAST(3.50 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (16, N'C2042', 3, CAST(4.00 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (17, N'C2042', 5, CAST(3.00 AS Decimal(3, 2)))
SET IDENTITY_INSERT [dbo].[StudentGrade] OFF
ALTER TABLE [dbo].[Course]  WITH CHECK ADD  CONSTRAINT [FK_Course_Department] FOREIGN KEY([DepartmentID])
REFERENCES [dbo].[Department] ([DepartmentID])
GO
ALTER TABLE [dbo].[Course] CHECK CONSTRAINT [FK_Course_Department]
GO
ALTER TABLE [dbo].[StudentGrade]  WITH CHECK ADD  CONSTRAINT [FK_StudentGrade_Student] FOREIGN KEY([StudentID])
REFERENCES [dbo].[Person] ([PersonID])
GO
ALTER TABLE [dbo].[StudentGrade] CHECK CONSTRAINT [FK_StudentGrade_Student]
GO

Next, compile and execute the following:

using System;
using System.Data;
using System.Data.SqlClient;
using System.Threading.Tasks;

class Program {

   static class SqlHelper {
      // Set the connection, command, and then execute the command with non query.
      public static Int32 ExecuteNonQuery(String connectionString, String commandText,
          CommandType commandType, params SqlParameter[] parameters) {
         using (SqlConnection conn = new SqlConnection(connectionString)) {
            using (SqlCommand cmd = new SqlCommand(commandText, conn)) {
               // There're three command types: StoredProcedure, Text, TableDirect. The TableDirect 
               // type is only for OLE DB.  
               cmd.CommandType = commandType;
               cmd.Parameters.AddRange(parameters);

               conn.Open();
               return cmd.ExecuteNonQuery();
            }
         }
      }

      // Set the connection, command, and then execute the command and only return one value.
      public static Object ExecuteScalar(String connectionString, String commandText,
          CommandType commandType, params SqlParameter[] parameters) {
         using (SqlConnection conn = new SqlConnection(connectionString)) {
            using (SqlCommand cmd = new SqlCommand(commandText, conn)) {
               cmd.CommandType = commandType;
               cmd.Parameters.AddRange(parameters);

               conn.Open();
               return cmd.ExecuteScalar();
            }
         }
      }

      // Set the connection, command, and then execute the command with query and return the reader.
      public static SqlDataReader ExecuteReader(String connectionString, String commandText,
          CommandType commandType, params SqlParameter[] parameters) {
         SqlConnection conn = new SqlConnection(connectionString);

         using (SqlCommand cmd = new SqlCommand(commandText, conn)) {
            cmd.CommandType = commandType;
            cmd.Parameters.AddRange(parameters);

            conn.Open();
            // When using CommandBehavior.CloseConnection, the connection will be closed when the 
            // IDataReader is closed.
            SqlDataReader reader = cmd.ExecuteReader(CommandBehavior.CloseConnection);

            return reader;
         }
      }
   }

   static void Main(string[] args) {
      String connectionString = "Data Source=(local);Initial Catalog=MySchool;Integrated Security=True;Asynchronous Processing=true;";

      CountCourses(connectionString, 2012);
      Console.WriteLine();

      Console.WriteLine("Following result is the departments that started from 2007:");
      GetDepartments(connectionString, 2007);
      Console.WriteLine();

      Console.WriteLine("Add the credits when the credits of course is lower than 4.");
      AddCredits(connectionString, 4);
      Console.WriteLine();

      Console.WriteLine("Please press any key to exit...");
      Console.ReadKey();
   }

   static void CountCourses(String connectionString, Int32 year) {
      String commandText = "Select Count([CourseID]) FROM [MySchool].[dbo].[Course] Where Year=@Year";
      SqlParameter parameterYear = new SqlParameter("@Year", SqlDbType.Int);
      parameterYear.Value = year;

      Object oValue = SqlHelper.ExecuteScalar(connectionString, commandText, CommandType.Text, parameterYear);
      Int32 count;
      if (Int32.TryParse(oValue.ToString(), out count))
         Console.WriteLine("There {0} {1} course{2} in {3}.", count > 1 ? "are" : "is", count, count > 1 ? "s" : null, year);
   }

   // Display the Departments that start from the specified year.
   static void GetDepartments(String connectionString, Int32 year) {
      String commandText = "dbo.GetDepartmentsOfSpecifiedYear";

      // Specify the year of StartDate
      SqlParameter parameterYear = new SqlParameter("@Year", SqlDbType.Int);
      parameterYear.Value = year;

      // When the direction of parameter is set as Output, you can get the value after 
      // executing the command.
      SqlParameter parameterBudget = new SqlParameter("@BudgetSum", SqlDbType.Money);
      parameterBudget.Direction = ParameterDirection.Output;

      using (SqlDataReader reader = SqlHelper.ExecuteReader(connectionString, commandText,
          CommandType.StoredProcedure, parameterYear, parameterBudget)) {
         Console.WriteLine("{0,-20}{1,-20}{2,-20}{3,-20}", "Name", "Budget", "StartDate",
             "Administrator");
         while (reader.Read()) {
            Console.WriteLine("{0,-20}{1,-20:C}{2,-20:d}{3,-20}", reader["Name"],
                reader["Budget"], reader["StartDate"], reader["Administrator"]);
         }
      }
      Console.WriteLine("{0,-20}{1,-20:C}", "Sum:", parameterBudget.Value);
   }

   // If credits of course is lower than the certain value, the method will add the credits.
   static void AddCredits(String connectionString, Int32 creditsLow) {
      String commandText = "Update [MySchool].[dbo].[Course] Set Credits=Credits+1 Where Credits<@Credits";

      SqlParameter parameterCredits = new SqlParameter("@Credits", creditsLow);

      Int32 rows = SqlHelper.ExecuteNonQuery(connectionString, commandText, CommandType.Text, parameterCredits);

      Console.WriteLine("{0} row{1} {2} updated.", rows, rows > 1 ? "s" : null, rows > 1 ? "are" : "is");
   }
}
Version Information

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1
Platforms

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Thread Safety
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.