public void DistinctCount()
{
var result = SelectAggregate("DISTINCT_COUNT", SqlExpression.Reference(new ObjectName("a")));
Assert.IsNotNull(result);
Assert.IsFalse(result.IsNull);
Assert.IsInstanceOf<NumericType>(result.Type);
Assert.IsInstanceOf<SqlNumber>(result.Value);
var value = (SqlNumber)result.Value;
Assert.AreEqual(new SqlNumber(15), value);
}