Ordinal values in C# SQL client

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I have a function

GetStudents

, that accepts two parameters. I want to use ordinal values to make the select but I am getting an error. If I manage to do this then I will try to add a where in clause that conditions vary that is why I need to use ordinal values.

using (SqlCommand cd = db.CreateCommand())
                    {
                        cd.CommandType = CommandType.Text;
                        cd.CommandText = "SELECT ClassName FROM GetStudents(?,?)";
                        cd.Parameters.AddWithValue(null, age);
                        cd.Parameters.AddWithValue(null, monthBday);
}

What I have tried:

<pre>using (SqlCommand cd = db.CreateCommand())
                    {
                        cd.CommandType = CommandType.Text;
                        cd.CommandText = "SELECT ClassName FROM GetStudents(?,?)";
                        cd.Parameters.AddWithValue(null, age);
                        cd.Parameters.AddWithValue(null, monthBday);
}

Posted 27-Feb-18 4:10am

datt265

Updated 27-Feb-18 4:27am

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Richard Deeming · Accepted Answer · 2018-02-27T04:14:00

Solution 1

SQL uses named parameters. For a function call, the parameter names don't need to match the names declared in the function:

C#

cd.CommandText = "SELECT ClassName FROM GetStudents(@p0,@p1)";
cd.Parameters.AddWithValue("@p0", age);
cd.Parameters.AddWithValue("@p1", monthBday);

Posted 27-Feb-18 4:14am

Richard Deeming

Comments

datt265 27-Feb-18 10:26am

Yes like this works, now If I want to add a where 'country' but county names can change how do I do it?

SELECT ClassName FROM GetStudents(?,?) where country in ('USA', 'UK')

Richard Deeming 27-Feb-18 10:32am

string[] countries = { "USA", "UK" };
string[] parameterNames = countries.Select((_, i) => "@C" + i).ToArray();

cd.CommandText = string.Format(
    "SELECT ClassName FROM GetStudents(@p0,@p1) WHERE country In ({0})",
    string.Join(", ", parameterNames));

// ==> "SELECT ClassName FROM GetStudents(@p0,@p1) WHERE country In (@C0, @C1)"

cd.Parameters.AddWithValue("@p0", age);
cd.Parameters.AddWithValue("@p1", monthBday);

for (int index = 0; index < countries.Length; index++)
{
    cd.Parameters.AddWithValue(parameterNames[index], countries[index]);
}

#realJSOP · Accepted Answer · 2018-02-27T04:27:00

I think your approach is all wrong. You can calculate their age with some SQL date math code. Beyond that, your GetStudents function should not even exist. Whatever query is in the function can be put into the query that's calling the function. Calling a function in a query is very expensive in terms of performance, and should be avoided if possible. So, assuming you want the classname for all students of a certain age:

SQL

SELECT [ClassName] 
FROM Students 
WHERE @age = DATEDIFF(YEAR, CONVERT(DATE,GETDATE()), CONVERT(DATE,[DateOfBirth]))