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(PHP 4, PHP 5)

pg_connectOpen a PostgreSQL connection


resource pg_connect ( string $connection_string [, int $connect_type ] )

pg_connect() opens a connection to a PostgreSQL database specified by the connection_string .

If a second call is made to pg_connect() with the same connection_string as an existing connection, the existing connection will be returned unless you pass PGSQL_CONNECT_FORCE_NEW as connect_type .

The old syntax with multiple parameters $conn = pg_connect("host", "port", "options", "tty", "dbname") has been deprecated.

Список параметров


The connection_string can be empty to use all default parameters, or it can contain one or more parameter settings separated by whitespace. Each parameter setting is in the form keyword = value. Spaces around the equal sign are optional. To write an empty value or a value containing spaces, surround it with single quotes, e.g., keyword = 'a value'. Single quotes and backslashes within the value must be escaped with a backslash, i.e., \' and \\.

The currently recognized parameter keywords are: host , hostaddr , port , dbname , user , password , connect_timeout , options , tty (ignored), sslmode , requiressl (deprecated in favor of sslmode ), and service . Which of these arguments exist depends on your PostgreSQL version.


If PGSQL_CONNECT_FORCE_NEW is passed, then a new connection is created, even if the connection_string is identical to an existing connection.

Возвращаемые значения

PostgreSQL connection resource on success, FALSE on failure.


Пример #1 Using pg_connect()

//connect to a database named "mary"

$dbconn2 pg_connect("host=localhost port=5432 dbname=mary");
// connect to a database named "mary" on "localhost" at port "5432"

$dbconn3 pg_connect("host=sheep port=5432 dbname=mary user=lamb password=foo");
//connect to a database named "mary" on the host "sheep" with a username and password

$conn_string "host=sheep port=5432 dbname=test user=lamb password=bar";
$dbconn4 pg_connect($conn_string);
//connect to a database named "test" on the host "sheep" with a username and password

Смотрите также

  • pg_pconnect() - Open a persistent PostgreSQL connection
  • pg_close() - Closes a PostgreSQL connection
  • pg_host() - Returns the host name associated with the connection
  • pg_port() - Return the port number associated with the connection
  • pg_tty() - Return the TTY name associated with the connection
  • pg_options() - Get the options associated with the connection
  • pg_dbname() - Get the database name

User Contributed Notes
gutostraube at gmail dot com
02-Oct-2009 01:51
It's possible connect to a PostgreSQL database via Unix socket using the pg_connect() function by the following two ways:

1) Using the socket path:

= pg_connect('host=/var/run/postgresql user=username dbname=databasename');

2) Omitting the host name/path:

= pg_connect('user=username dbname=databasename');

Note: in this case (omitting the host value), the default socket path will be used.
28-Aug-2009 10:57
If the configuration parameter "ssl = true" is set in postgres.conf, and a pg_connect() is done without "sslmode=disable", then the connection seems to be established with SSL by default. Enabling SSL in Postgres can cause performance problems with large data transfers (e.g. bytea), because Postgres has a "built-in" native SSL Support, so Postgres has to do all the encryption.
bgalloway at citycarshare dot org
28-Mar-2008 02:33
Beware about writing something like
function getdb_FAILS() {
pg_connect("...") or die('connection failed');

It will return a boolean.  This will appear to be fine if you don't use the return value as a db connection handle, but will fail if you do.

Instead, use:
function getdb() {
$db = pg_connect("...") or die('connection failed');

which actually returns a handle.
tim at buttersideup dot com
28-Dec-2007 06:41
It's not explicitly stated here, but you can also connect to PostgreSQL via a UNIX domain socket by leaving the host empty.  This should have less overhead than using TCP e.g.:

$dbh = new PDO('pgsql:user=exampleuser dbname=exampledb password=examplepass');

In fact as the C library call PQconnectdb underlies this implementation, you can supply anything that this library call would take - the "pgsql:" prefix gets stripped off before PQconnectdb is called, and if you supply any of the optional arguments (e.g. user), then these arguments will be added to the string that you supplied...  Check the docs for your relevant PostgreSQL client library: e.g.


If you really want, you can use ';'s to separate your arguments - these will just be converted to spaces before PQconnectdb is called.

20-Aug-2007 04:17
remember that when you use a blank password there will be an error because of:
password= dbname= (...)
to fix this problem use '' in your $options variable

$options = " host='localhost' port='5432' user='postgres' password='' dbname='test' ";

*** careful: I used double ' after password=, not "
Sohel Taslim
03-Aug-2007 02:20
I got the same problem but I have to solve that in different way.
In my postgresql.conf file the following was commented.
So, I active that under Connection Settings-

# - Connection Settings �_"
tcpip_socket = true
borovik -at- gmail
03-Apr-2007 02:06
"If you use pg_connect('host=localhost port=5432 user=my_username password=my_password dbname=my_dbname') and you get the following error:
"Warning: pg_connect(): Unable to connect to PostgreSQL server: could not connect to server: Connection refused Is the server running on host localhost and accepting TCP/IP connections on port 5432?"
I solved this error just by setting listen_addresses = '*' in the postgresql.conf file. This error occurs probably despite of a name resolution to localhost, given in the "host" parameter. So you can set the host in the pg_connect() function.
10-Apr-2005 04:51
The values accepted by pg_connect's sslmode argument are: disable, allow, prefer, require
phpnet at benjamin dot schulz dot name
01-Sep-2004 11:28
if you need to open a new connection handle (i.e. for multiple pg_send_query()) use PGSQL_CONNECT_FORCE_NEW as second parameter to pg_connect()
15-Dec-2003 09:47
If you use pg_connect('host=localhost port=5432 user=my_username password=my_password dbname=my_dbname') and you get the following error:
"Warning: pg_connect(): Unable to connect to PostgreSQL server: could not connect to server: Connection refused Is the server running on host localhost and accepting TCP/IP connections on port 5432?"
then you should try to leave the host= and port= parts out of the connection string. This sounds strange, but this is an "option" of Postgre. If you have not activated the TCP/IP port in postgresql.conf then postgresql doesn't accept any incoming requests from an TCP/IP port. If you use host= in your connection string you are going to connect to Postgre via TCP/IP, so that's not going to work. If you leave the host= part out of your connection string you connect to Postgre via the Unix domain sockets, which is faster and more secure, but you can't connect with the database via any other PC as the localhost.
xzilla at users dot sourceforge dot net
09-Dec-2003 04:22
regarding the note from  matias at nospam dot projectcast dot com
on 12-Feb-2002 01:16, you do not need a user in the database with the same name a your web user with ANY version of postgresql.  The only time that would be a requirement ifs if you set your postgresql server to only allow IDENT based authentication  (which IIRC is the default on Red Hat systems, which might be what lead to the confusion).  For more info on the various authentication methods allowed by postgresql, check out http://www.postgresql.org/docs/7.4/static/client-authentication.html
derry at siliconriver.com dot au
08-Aug-2003 03:48
pg_connect seems to support SSL connections, on systems where Postgres has been compiled with ssl, i'm assuming this is since psql uses libpq to connect.
pg_connect can successfully connect, and use the "requiressl" argument.
jtate at php dot net
31-Dec-2002 10:36
If you use host=HOSTNAME in your pg_connect string when connecting to PostgreSQL databases newer than 7.1, you need to make sure that your postmaster daemon is started with the "-i" option.  Otherwise the connection will fail.  See http://www.postgresql.org/idocs/index.php?client-authentication.html for client authentication documentation.
khyri at khyri dot com
01-Nov-2002 12:23
After upgrading to PHP 4.2.3 from PHP 4.1.2 (Red Hat Linux Advanced Server with Stronghold 4.0) in order to manually compile in MHASH support, I discovered that Postgres support has disappeared, despite being specified on the command line, and compiling with no errors.

FATAL: Undefined function: pg_connect()

Confirmed by looking at the output of phpinfo() and comparing it to the output pre-upgrade - no mention of PostgreSQL in the new one.

Detective work led me to find that the old pgsql.so in /usr/lib/php4 was untouched, and the new one had ended up in /usr/lib/20020429 instead.

The fix was to edit config_vars.mk after configuration to change the value of EXTENSION_DIR, and then compile.

Not quite sure where 20020429 came from, looks like a left-over value from development testing...

Anyway, in case any one else has a similar problem, thought I'd document it here, as a problem with pg_connect is where this will first surface as a symptom.
Helio Ferenhof <d-m at eudoramail dot com>
18-Feb-2002 09:20
Connection Hint:
Do you always write at the code the username and password to connect to your PostgreSQL database !?
What if your username or password changes?

Create a connection include file.

= pg_connect("host=localhost port=5432 dbname=DATABASENAME user=USERNAME password=PASSWORD")
      or die (
"Nao consegui conectar ao PostGres --> " . pg_last_error($conn));

// you can use $database name and pass it from the php file if you connect into different databases.


include('connection.php'); // Include the connection to the databank THEN start your SQL Job :)

$result=pg_exec("SELECT field FROM table WHERE field = '$something' "); // Sample of SQL QUERY
$fetch = pg_fetch_row($query_st); // Sample of SQL QUERY

pg_close($connection); // Close this connection

Helio Ferenhof
matias at nospam dot projectcast dot com
12-Feb-2002 09:16
At least with Postgres 7.2, connecting to local postgresdatabase requires a user in the database with the same name as the user running apache, or the connection fails.
rolf at sir-wum dot de
13-Oct-2001 12:54
pg_connect() won't work with the authentication method 'crypt' in the pg_hba.conf. Took me an hour to figure that out till I remeberd some other issues with windows missing the crypt() call.
kayotix at yahoo dot com
15-Sep-2000 06:54
Little note that is buried in the install somewhere.  In Php 3, PostgreSQL support was activated by adding --with-postgresql=[DIR] to the options passed to ./configure.  With Php 4.0.2 (on Linux) the parameter was --with-pgsql.  The only place I found this was in the installing PHP on Unix section of the manual.
leace at post dot cz
21-Jul-2000 09:26
If you use PostgreSQL users for authenticating into your pg database rather than using your own authentication, always specify host directive in pg_connect and edit pg_hba.conf to authenticate from this host accordingly. Otherwise, PHP will connect as 'local' using UNIX domain sockets, which is set in pg_hba.conf to 'trust' by default (so you can connect using psql on console without specifying password) and everyone can connect to db _without password_ .

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