Question

I used the following statement for a parameter.

comm.Parameters.Add("@name", SqlDbType.NVarChar, 50).Value = txtname.Text;

Name is a SQL Server nvarchar column but I get this error:

Error converting data type nvarchar to numeric.

My sql:

SqlCommand comm = conn.CreateCommand();
comm.CommandText = "execute addName @name";
comm.Parameters.Add("@name", SqlDbType.NVarChar, 50).Value = txtname.Text;

conn.Open();
comm.ExecuteNonQuery();
conn.Close();

Can help my to fix this problem?
My store procedure:

USE [info]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER procedure [dbo].[addName]
            @id numeric(18,0) = 0,
            @name nchar(50)
as
if (select name from TName where name = @name) is null
begin
select @id =  MAX(id)+1 from TName
insert into TName
values (@id, @name)
print @id
end
else
begin
print 'Eroare'
end

Answer 1

With the edit, with the signature:

ALTER procedure [dbo].[addName]
        @id numeric(18,0) = 0,
        @name nchar(50)

then the problem becomes clear:

execute addName @name

is pass-by-position – so you are passing the value of @name into the @id parameter. If you were calling this from TSQL, to pass-by-name you need to use:

execute addName @name = @name

The first (left) states the parameter name, the second (right) states the value to use for this parameter; for example, to pass a literal into addName‘s @name parameter:

execute addName @name = 'Fred'

However, from ADO.NET, a better approach is:

comm.CommandText = "addName";
comm.CommandType = CommandType.StoredProcedure;

which automatically treats it as an SP-exec using pass-by-name.