How to get count of rows from datareader ? read top 5 elements from datareader?

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I want to check how many rows in datareader[0] . and add top 5 numbers of data to listbox

What I have tried:

string query2 = "select Distinct OuterCode,OuterCode_Result,MasterCode,PalletCode from BatchDetails Where OuterCode_Result = 1 and " +
" MasterCode IS NULL and PalletCode IS NULL";

var dataReader = sqlDataReader1;

 while (dataReader.Read())

Posted 30-May-21 1:04am

Member 15212425

Updated 30-May-21 4:01am

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Richard MacCutchan 30-May-21 7:41am

What is the problem? Please show the complete code and explain what results you get.

Member 15212425 30-May-21 8:02am

I want to check if datareader[0] count is greater than rowcount..
when fetching distinct values only ,dr[0] doesnt have rowcount number of data

int rowcount = Convert.ToInt32(Settings.Default["outercode"]);
string query2 = string.Format($" select Distinct top({ rowcount}) OuterCode,OuterCode_Result,MasterCode,PalletCode from BatchDetails Where OuterCode_Result = 1 and " +
" MasterCode IS NULL and PalletCode IS NULL");
using (SqlCommand sqlCommand = new SqlCommand(query2, sqlConn3))
{
sqlCommand.Parameters.AddWithValue("@OuterCode_Result", 1);
sqlCommand.Parameters.AddWithValue("@MasterCode", "NULL");
sqlCommand.Parameters.AddWithValue("@PalletCode", "NULL");
//sqlCommand.Parameters.Add(textBox2.Text,SqlDbType.Int);

SqlDataReader sqlDataReader1 = sqlCommand.ExecuteReader();

var dataReader = sqlDataReader1;

while (dataReader.Read())
{
if (datareader[0].count >= rowcount ){
listBox1.Items.Add(dataReader[0]);}
}

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OriginalGriff · Answer 1 · 2021-05-30T04:01:00

DataReaders don't return a row count, because they don't return all the rows at once.
To find out how many rows you are going to get, you'd either have to read all the rows and count them then do your processing to read the rows again, or run a SELECT COUNT(*) FROM query before you issue the SELECT command to get the DataReader itself - and both solutions may return a different number of rows to those returned by your final DataReader because SQL Server is a multiuser system and the number of rows could easily change.

If you need to know how many rows, use a DataAdapter to fill a DataTable instead of a DataReader as that returns when all the rows are ready and supports a count.

If you only want up to five rows, then modify your query to retrieve only the ones you want:

SQL

SELECT TOP 5 DISTINCT ...

And add an ORDER BY clause or SQL can return rows in any order it deems fit.