DbTusk.cs

using System.Data;
using Npgsql;
namespace DbTusk;

class Program
{
    private const string connString =
        " ";

    static void Main(string[] args)
    {
        var tables = new List<Tables>();

        var connection = new NpgsqlConnection(connString);

        try
        {
            var query = @"select * from ""EZ_tables"".""Teachers"";
                          select * from ""EZ_tables"".""Students"";
                          select * from ""EZ_tables"".""Subjects"";";
            var command = new NpgsqlCommand(query, connection);

            connection.Open();

            var reader = command.ExecuteReader();

            while (reader.Read())
            {
                tables.Add(new Tables
                {
                    TeacherName = reader.GetString("Teacher"),
                    StudentName = reader.GetString("Student"),
                    SubjectName = reader.GetString("Subject")
                });
            }

            reader.Close();
            command.Dispose();

            tables.ForEach(select => Console.WriteLine($" {select.SubjectName} : {select.TeacherName} : {select.StudentName}"));
        }

        finally
        {
            if (connection.State == ConnectionState.Open)
                connection.Close();
        }
    }

    public class Tables
    {
        public int Id { get; init; }

        public string TeacherName { get; init; } = default!;

        public string StudentName { get; init; } = default!;

        public string SubjectName { get; init; } = default!;
    }
}