var connection = PostgreSQLConnection("localhost", 5432, "dart_test", username: "dart", password: "dart");
await connection.open();

List<List<dynamic>> results = await connection.query("SELECT a, b FROM table WHERE a = @aValue", substitutionValues: {
    "aValue" : 3
});
for (final row in results) {
  var a = row[0];
  var b = row[1];
} 

List<Map<String, Map<String, dynamic>>> results = await connection.mappedResultsQuery(
  "SELECT t.id, t.name, u.name FROM t LEFT OUTER JOIN u ON t.id=u.t_id");
for (final row in results) {
  var tID = row["t"]["id"];
  var tName = row["t"]["name"];
  var uName = row["u"]["name"];
}

await connection.transaction((ctx) async {
    var result = await ctx.query("SELECT id FROM table");
    await ctx.query("INSERT INTO table (id) VALUES (@a:int4)", substitutionValues: {
        "a" : result.last[0] + 1
    });
});