CREATE TABLE dbo.TableUser (
  Login               VARCHAR(50),
  PasswordHash        VARCHAR(50)
)
GO

SET NOCOUNT ON

INSERT INTO TableUser VALUES ('Vasya', '3fde6bb0541387e4ebdadf7c2ff31123')
INSERT INTO TableUser VALUES ('Petya', '00a1f187721c63501356bf791e69382c')
INSERT INTO TableUser VALUES ('Masha', '8bd6a8b9a8a5573e5a625a28e106dab2')

SET NOCOUNT OFF
GO

CREATE PROCEDURE dbo.CheckUserWithSpecifiedPasswordExists (
  @p_sPasswordHash    VARCHAR(50)
)
AS
BEGIN
  IF EXISTS (SELECT 1 FROM TableUser WHERE PasswordHash = @p_sPasswordHash)
    RETURN 1
    
  RETURN 0
END
GO

DECLARE @nReturnValue INTEGER

EXEC @nReturnValue = CheckUserWithSpecifiedPasswordExists '3fde6bb0541387e4ebdadf7c2ff31123'
PRINT @nReturnValue -- 1 - есть

EXEC @nReturnValue = CheckUserWithSpecifiedPasswordExists 'ebdadf7c2ff311233fde6bb0541387e4'
PRINT @nReturnValue -- 0 - нет
GO

DROP PROCEDURE dbo.CheckUserWithSpecifiedPasswordExists
DROP TABLE dbo.TableUser
GO

 SqlConnection conn = null;
            SqlDataReader rdr = null;
            

            conn = new SqlConnection("Data Source=(LocalDB)\\v11.0;AttachDbFilename=C:\\Users\\trutn_000\\Documents\\DbProWizardMain.mdf;User ID=User;Password=100Million;Connect Timeout=30");
            conn.Open();

            // 1.  create a command object identifying the stored procedure
            SqlCommand cmd = new SqlCommand("CheckUserEmail", conn);

            // 2. set the command object so it knows to execute a stored procedure
            cmd.CommandType = CommandType.StoredProcedure;

            // 3. add parameter to command, which will be passed to the stored procedure
            cmd.Parameters.Add(new SqlParameter("@Email", 1));

            // execute the command
            rdr = cmd.ExecuteReader();

                 conn.Close();

CREATE PROCEDURE dbo.CheckUserEmail (
  @Email    VARCHAR(50)
)
AS
BEGIN
  IF EXISTS (SELECT 1 FROM TableUser WHERE Email = @Email)
    RETURN 1
    
  RETURN 0
END

CREATE TABLE [dbo].[TableUser] (
    [IdUser]    INT           NULL,
    [Email]     NVARCHAR (50) NULL,
    [Passwort]  NVARCHAR (50) NULL,
    [IdSession] NVARCHAR (50) NULL
);