@title epgsql - PostgreSQL driver for Erlang
@doc
== Interfaces ==
Epgsql has 3 API interfaces:

<ul>
  <li>{@link epgsql} - synchronous</li>
  <li>{@link epgsqla} - asynchronous</li>
  <li>{@link epgsqli} - incremental</li>
</ul>

They have the same set of functions, but differ by the way they deliver results.

`epgsql' returns results as a function's return value;
`epgsqla' delivers whole result as a single message;
`epgsqli' delivers results and metadata in individual messages row-by-row.

It's usualy not a problem to use different interfaces with the same connection.

== Example session ==

```
{ok, C} = epgsql:connect(#{host => "localhost",
                           username => "test-user", password => "test",
                           database => "test-db"}),
{ok, _Columns, Rows} = epgsql:equery(C, "SELECT * FROM users WHERE id=$1", [42]),
io:format("Users: ~p~n", [Rows]),

Ref = epgsqla:squery(C, "SELECT count(*) FROM users"),
receive
  {C, Ref, {ok, [#column{}], [{Count}]}} ->
    io:format("count: ~p~n", [binary_to_integer(Count)]);
  {C, Ref, #error{} = E} ->
    io:format("error: ~p~n", [E])
after 10000 ->
    io:format("timeout"),
    ok = epgsql:cancel(C),
    % we still can receive normal result because `cancel' is always asynchronous
    % otherwise we will receive
    % `#error{code = <<"57014">>, codename = query_canceled}'
    receive {C, Ref, OkOrCancel} ->
      io:format("cancelation result: ~p~n", [OkOrCancel])
    end
end,
ok =
 epgsql:with_transaction(
   C,
   fun() ->
     [{ok, _}, {ok, _}] =
       epgsql:execute_batch(
         C, "INSERT INTO users (name, age) VALUES ($1, $2)",
         [
          [<<"Joe">>, 35],
          [<<"Mary">>, 24]
         ]),
     ok
   end, #{}),
ok = epgsql:close(C).
'''

== Commands ==

Client can execute a number of built-in commands as well as define
their own. See {@link epgsql_command}.

== Datatypes ==

Epgsql supports both text and binary data encodings. There are a bunch
of built-in codecs and it's possible to implement custom ones
as well as fine-tune some of built-ins. See {@link epgsql_codec}.