c# ExecuteNonQuery always returns Zero

Question

I think nothing's wrong with the connection because when I open it, it does not throw any error. So I guess the error is when I'm executing a command. This is my code:

OleDbCommand cmd = new OleDbCommand("SELECT * FROM cars", conn);
cmd.CommandType = CommandType.Text;
int numbers = cmd.ExecuteNonQuery();

I tried using a message box to display the value of numbers but the result is always 0. The table cars contains 5 records. So why am I not getting the correct results?..

Answer 1

To the anonymous downvoter, the key part of the OP:

I tried using a message box to display the value of numbers but the result is always 0. The table cars contains 5 records. So why am I not getting the correct results?..

The OP is obviously trying to get a count of records in the table (a scalar aggregate) and not all of the table data.

My answer:

That's because your query is returning a table and not a scalar value and you're calling the incorrect function. Your query should be should be:

"SELECT COUNT(*) FROM cars"

And ExecuteNonQuery doesn't actually expect any results to be returned. (You usually run insert, update and delete operations with ExecuteNonQuery.) You should be using ExecuteScalar which expects a single-valued result such as count(*).

All together now:

OleDbCommand cmd = new OleDbCommand("SELECT count(*) FROM cars", conn);
cmd.CommandType = CommandType.Text;
int numbers = cmd.ExecuteScalar();

Answer 2

Try using ExecuteScalar that should give you the count. ExecuteNonQuery doesn't return the results from your query. The return your looking at indicates how many rows were affected by your statement, in your case zero.

Answer 3

ExecuteNonQuery as the name tells you does not make a query. it is normally used for inserts or updates and returns the number of affected records. for the query you provided you should use ExecuteReader or a DataAdapter and its Fill method to fill a datatable.

Answer 4

Because you are executing a query, and ExecuteNonQuery returns the number of rows effected, which when you select is always 0 since you aren't changing anything (ie. INSERT,UPDATE or DELETE)

Answer 5

ExecuteNonQuery only returns the number of rows affected for UPDATE, DELETE or INSERT operations. For the number of rows in the SELECT statement, try:

OleDbCommand cmd = new OleDbCommand("SELECT * FROM cars", conn);
OleDbDataReader reader = cmd.ExecuteReader();

int numbers = 0;
while (reader.Read())
{
    //// other Reader-related operations here...

    numbers++;
}