Erlang PostgreSQL Database Client

* Connect

  {ok, C} = pgsql:connect(Host, [Username], [Password], Opts).

  Host      - host to connect to.
  Username  - username to connect as, defaults to $USER.
  Password  - optional password to authenticate with.
  Opts      - property list of extra options. Supported properties:

    + database
    + port
    + ssl (true | false | required)
    + ssl_opts (see ssl docs in OTP)
    + timeout (milliseconds, defaults to 5000)

  {ok, C} = pgsql:connect("localhost", "username", [{database, "test_db"}]).
  ok = pgsql:close(C).

  The timeout parameter is applied to all operations. In the case of equery
  this means that total execution time may exceed the timeout value.

* Simple Query

  {ok, Columns, Rows}        = pgsql:squery(C, "select ...").
  {ok, Count}                = pgsql:squery(C, "update ...").
  {ok, Count, Columns, Rows} = pgsql:squery(C, "insert ... returning ...").

  {error, Error}             = pgsql:squery(C, "invalid SQL").

  Columns       - list of column records, see pgsql.hrl for definition.
  Rows          - list of tuples, one for each row.
  Count         - integer count of rows inserted/updated/etc

  The simple query protocol returns all columns as text (Erlang binaries)
  and does not support binding parameters.

* Extended Query

  {ok, Columns, Rows}        = pgsql:equery(C, "select ...", [Parameters]).
  {ok, Count}                = pgsql:equery(C, "update ...", [Parameters]).
  {ok, Count, Columns, Rows} = pgsql:equery(C, "insert ... returning ...", [Parameters]).

  {error, Error}             = pgsql:equery(C, "invalid SQL", [Parameters]).

  Parameters    - optional list of values to be bound to $1, $2, $3, etc.

  The extended query protocol combines parse, bind, and execute using
  the unnamed prepared statement and portal. A "select" statement returns
  {ok, Columns, Rows}, "insert/update/delete" returns {ok, Count} or
  {ok, Count, Columns, Rows} when a "returning" clause is present. When
  an error occurs, all statements result in {error, #error{}}.

  PostgreSQL's binary format is used to return integers as Erlang
  integers, floats as floats, bytea/text/varchar columns as binaries,
  bools as true/false, etc. For details see pgsql_binary.erl and the
  Data Representation section below.

* Parse/Bind/Execute

  {ok, Statement} = pgsql:parse(C, [StatementName], Sql, [ParameterTypes]).

  StatementName   - optional, reusable, name for the prepared statement.
  ParameterTypes  - optional list of PostgreSQL types for each parameter.

  For valid type names see pgsql_types.erl.

  ok = pgsql:bind(C, Statement, [PortalName], ParameterValues).

  PortalName      - optional name for the result portal.

  {ok | partial, Rows} = pgsql:execute(C, Statement, [PortalName], [MaxRows]).
  {ok, Count}          = pgsql:execute(C, Statement, [PortalName]).
  {ok, Count, Rows}    = pgsql:execute(C, Statement, [PortalName]).

  PortalName      - optional portal name used in bind/4.
  MaxRows         - maximum number of rows to return (0 for all rows).

  execute returns {partial, Rows} when more rows are available.

  ok = pgsql:close(C, Statement).
  ok = pgsql:close(C, statement | portal, Name).
  ok = pgsql:sync(C).

  All functions return {error, Error} when an error occurs.

* Data Representation

  null        = null
  bool        = true | false
  char        = $A | binary
  intX        = 1
  floatX      = 1.0
  date        = {Year, Month, Day}
  time        = {Hour, Minute, Second.Microsecond}
  timetz      = {time, Timezone}
  timestamp   = {date, time}
  timestamptz = {date, time}
  interval    = {time, Days, Months}
  text        = <<"a">>
  varchar     = <<"a">>
  bytea       = <<1, 2>>

  record      = {int2, time, text, ...} (decode only)

* Errors

  Errors originating from the PostgreSQL backend are returned as {error, #error{}},
  see pgsql.hrl for the record definition. epgsql may also return {error, Atom}
  where Atom is 'timeout' or 'closed'.