How to use executeReader() method to retrieve the value of just one cell

Question

I need to execute the following command and pass the result to a label. I don't know how can i do it using Reader. Someone can give me a hand?

String sql = "SELECT * FROM learer WHERE learer.id = " + index;
SqlCommand cmd = new SqlCommand(sql,conn);
learerLabel.Text = (String) cmd.ExecuteReader();

As you can see i create the SQL statement and i execute it, but it does not work. Why?

The console says:

Cannot implicitly SqlDataReader to String...

How can i get the desired results as String so the label can display it properly.

possible duplicate of [Using select count(\*) in c#](http://stackoverflow.com/questions/5701910/using-select-count-in-c-sharp) — Qantas 94 Heavy, Apr 15 '14 at 07:48

score 50 · Answer 1 · answered Apr 26 '11 at 18:10

50

using (var conn = new SqlConnection(SomeConnectionString))
using (var cmd = conn.CreateCommand())
{
    conn.Open();
    cmd.CommandText = "SELECT * FROM learer WHERE id = @id";
    cmd.Parameters.AddWithValue("@id", index);
    using (var reader = cmd.ExecuteReader())
    {
        if (reader.Read())
        {
            learerLabel.Text = reader.GetString(reader.GetOrdinal("somecolumn"))
        }
    }
}

answered Apr 26 '11 at 18:10

Darin Dimitrov

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"reader.GetString(reader.GetOrdinal("somecolumn"))" is the easiest way to retrieve a text value ? there's nothing like reader.fieldByName("Name").asString ? – Rebelss Jan 24 '14 at 22:25
3

Thank you for showing me how to use `ExecuteReader()` and not Scalar as the question asked – AlbatrossCafe Nov 06 '15 at 22:19
side note you cannot do this with table names just the variables – Robot70 Jun 21 '17 at 20:51

score 29 · Accepted Answer · edited Apr 11 '18 at 03:15

29

It is not recommended to use DataReader and Command.ExecuteReader to get just one value from the database. Instead, you should use Command.ExecuteScalar as following:

String sql = "SELECT ColumnNumber FROM learer WHERE learer.id = " + index;
SqlCommand cmd = new SqlCommand(sql,conn);
learerLabel.Text = (String) cmd.ExecuteScalar();

Here is more information about Connecting to database and managing data.

edited Apr 11 '18 at 03:15

Mukus

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answered Apr 26 '11 at 18:11

Akram Shahda

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`"SELECT ColumnNumber FROM learer WHERE learer.id = " + index` may have a [SQL injection attack](https://en.wikipedia.org/wiki/SQL_injection) vulnerability. Instead use a parameterized query as shown in e.g. [this answer](https://stackoverflow.com/a/5794580/3744182/3744182). See: [Why do we always prefer using parameters in SQL statements?](https://stackoverflow.com/q/7505808/3744182) and also https://software-security.sans.org/developer-how-to/fix-sql-injection-microsoft-.net-with-parameterized-queries – dbc Jan 17 '20 at 21:46

score 2 · Answer 3 · answered Apr 27 '11 at 09:38

2

ExecuteScalar() is what you need here

answered Apr 27 '11 at 09:38

iTSrAVIE

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score 0 · Answer 4 · edited May 23 '17 at 12:33

0

Duplicate question which basically says use ExecuteScalar() instead.

edited May 23 '17 at 12:33

Community

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answered Apr 26 '11 at 18:09

m.edmondson

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How to use executeReader() method to retrieve the value of just one cell

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