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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, String}
+ {port, Integer}
+ {ssl, Atom} true | false | required
+ {ssl_opts, List} see ssl application docs in OTP
+ {timeout, Integer} milliseconds, defaults to 5000
+ {async, Pid} see Asynchronous Messages section
{ok, C} = pgsql:connect("localhost", "username", [{database, "test_db"}]).
ok = pgsql:close(C).
The timeout parameter will trigger an {error, timeout} result when the
server fails to respond within Timeout milliseconds. This timeout applies
to the initial connection attempt and any subsequent queries.
* 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>>
array = [1, 2, 3]
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 functions may also return
{error, What} where What is one of the following:
{unsupported_auth_method, Method} - required auth method is unsupported
timeout - request timed out
closed - connection was closed
sync_required - error occured and pgsql:sync must be called
* Asynchronous Messages
PostgreSQL may deliver two types of asynchronous message: "notices" in response
to notice and warning messages generated by the server, and "notifications" which
are generated by the LISTEN/NOTIFY mechanism.
Passing the {async, Pid} option to pgsql:connect will result in these async
messages being sent to the specified process, otherwise they will be dropped.
Message formats:
{pgsql, Connection, {notification, Channel, Pid, Payload}}
Connection - connection the notification occured on
Channel - channel the notification occured on
Pid - database session pid that sent notification
Payload - optional payload, only available from PostgreSQL >= 9.0
{pgsql, Connection, {notice, Error}}
Connection - connection the notice occured on
Error - an #error{} record, see pgsql.hrl