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//
// Test/ExecuteScalar.cs
//
// Test the ExecuteScalar method in the
// System.Data.SqlClient.SqlCommand class
//
// ExecuteScalar is meant to be lightweight
// compared to ExecuteReader and only
// returns one column and one row as one object.
//
// It is meant for SELECT SQL statements that
// use an aggregate/group by function, such as,
// count(), sum(), avg(), min(), max(), etc...
//
// The object that is returned you do an
// explicit cast. For instance, to retrieve a
// Count of rows in a PostgreSQL table, you
// would use "SELECT COUNT(*) FROM SOMETABLE"
// which returns a number of oid type 20 which is
// a PostgreSQL int8 which maps to
// the .NET type System.Int64. You
// have to explicitly convert this returned object
// to the type you are expecting, such as, an Int64
// is returned for a COUNT().
// would be:
// Int64 myCount = (Int64) cmd.ExecuteScalar(selectStatement);
//
// Author:
// Daniel Morgan <danmorg@sc.rr.com>
//
// (C) 2002 Daniel Morgan
//
using System;
using System.Data;
using System.Data.SqlClient;
namespace TestSystemDataSqlClient
{
class TestSqlDataReader
{
static void Test() {
SqlConnection con = null;
SqlCommand cmd = null;
String connectionString = null;
String sql = null;
connectionString =
"host=localhost;" +
"dbname=test;" +
"user=postgres";
try {
string maxStrValue;
con = new SqlConnection(connectionString);
con.Open();
// test SQL Query for an aggregate count(*)
sql = "select count(*) " +
"from sometable";
cmd = new SqlCommand(sql,con);
Console.WriteLine("Executing: " + sql);
Int64 rowCount = (Int64) cmd.ExecuteScalar();
Console.WriteLine("Row Count: " + rowCount);
// test SQL Query for an aggregate min(text)
sql = "select max(tdesc) " +
"from sometable";
cmd = new SqlCommand(sql,con);
Console.WriteLine("Executing: " + sql);
string minValue = (string) cmd.ExecuteScalar();
Console.WriteLine("Max Value: " + minValue);
// test SQL Query for an aggregate max(text)
sql = "select min(tdesc) " +
"from sometable";
cmd = new SqlCommand(sql,con);
Console.WriteLine("Executing: " + sql);
maxStrValue = (string) cmd.ExecuteScalar();
Console.WriteLine("Max Value: " + maxStrValue);
// test SQL Query for an aggregate max(int)
sql = "select min(aint4) " +
"from sometable";
cmd = new SqlCommand(sql,con);
Console.WriteLine("Executing: " + sql);
int maxIntValue = (int) cmd.ExecuteScalar();
Console.WriteLine("Max Value: " + maxIntValue.ToString());
// test SQL Query for an aggregate avg(int)
sql = "select avg(aint4) " +
"from sometable";
cmd = new SqlCommand(sql,con);
Console.WriteLine("Executing: " + sql);
decimal avgDecValue = (decimal) cmd.ExecuteScalar();
Console.WriteLine("Max Value: " + avgDecValue.ToString());
// test SQL Query for an aggregate sum(int)
sql = "select sum(aint4) " +
"from sometable";
cmd = new SqlCommand(sql,con);
Console.WriteLine("Executing: " + sql);
Int64 summed = (Int64) cmd.ExecuteScalar();
Console.WriteLine("Max Value: " + summed);
// test a SQL Command is (INSERT, UPDATE, DELETE)
sql = "insert into sometable " +
"(tid,tdesc,aint4,atimestamp) " +
"values('qqq','www',234,NULL)";
cmd = new SqlCommand(sql,con);
Console.WriteLine("Executing: " + sql);
object objResult1 = cmd.ExecuteScalar();
if(objResult1 == null)
Console.WriteLine("Result is null. (correct)");
else
Console.WriteLine("Result is not null. (not correct)");
// test a SQL Command is not (INSERT, UPDATE, DELETE)
sql = "SET DATESTYLE TO 'ISO'";
cmd = new SqlCommand(sql,con);
Console.WriteLine("Executing: " + sql);
object objResult2 = cmd.ExecuteScalar();
if(objResult2 == null)
Console.WriteLine("Result is null. (correct)");
else
Console.WriteLine("Result is not null. (not correct)");
}
catch(Exception e) {
Console.WriteLine(e.ToString());
}
finally {
if(con != null)
if(con.State == ConnectionState.Open)
con.Close();
}
}
[STAThread]
static void Main(string[] args)
{
Test();
}
}
}
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