Simple Connection to PostgreSQL

Like MySQL, the PostgreSQL database is quite popular among PHP developers. Understandably, there are numerous well-documented PHP functions you can use in conjunction with PostgreSQL; see the PHP Manual for a complete list. However, you only need a few of these functions in order to make a simple connection and select some data:

pg_connect - opens a connection to PostgreSQL; requires a hostname, database name, username and password.

pg_exec - executes the SQL statement.

pg_numrows - returns the number of rows in a result.

pg_fetch_array - puts a SQL statement result row in an array.

pg_freeresult - frees the resources in use by the current connection.

pg_close - closes the current connection.

Just for argument's sake, let's pretend that a PostgreSQL database is already installed on your system, for which you have a valid username and password. Let's also assume that you've created a table on that database, called COFFEE_INVENTORY. The COFFEE_INVENTORY table has three columns: COFFEE_NAME, ROAST_TYPE and QUANTITY.

+-------------------+-------------+-----------+
|  COFFEE_NAME      | ROAST_TYPE  | QUANTITY  |
+-------------------+-------------+-----------+
|  French Roast     | dark        | 18        |
|  Kenya            | medium      | 6         |
|  Ethiopian Harrar | medium      | 35        |
|  Sumatra          | dark        | 8         |
|  Columbian        | light       | 12        |
+-------------------+-------------+-----------+

Now, let's do some PHP. Before you begin, you must know the name of the server on which the database resides, and have a valid username and password. Then, start your PHP code by creating a connection variable:

The die() function is used to stop the script and print a given error message, should the previous function fail (in this case, if a connection was not made.)
 
Up to this point, you've told PHP to connect to a server and select a database. If you've made it this far, you can issue a SQL statement and hopefully see some results! Using the COFFEE_INVENTORY table, suppose you want to view your inventory, including the name of the coffee and the roast type, with the highest number of bags listed first. Create a variable that holds your SQL statement: 
$sql = "SELECT COFFEE_NAME, ROAST_TYPE, QUANTITY
 	FROM COFFEE_INVENTORY
	ORDER BY QUANTITY DESC";

Next, create a variable to hold the result of the query, carried out by the pg_exec function. The pg_exec function takes two arguments: the connection and SQL statement variables you've just created. 
$sql_result = pg_exec($connection,$sql)
	or die("Couldn't execute query.");

Get the number of rows in the result set, using the pg_numrows function:
 
$num = pg_numrows($sql_result);
 
To format the results currently held in $sql_result, first separate the results by row, using the pg_fetch_array function inside a while loop:
$i = 0;

while ($i < $num) {
	$row = pg_fetch_array($sql_result, $i);

		// more code here...	
	
	$i++;
}

The while loop will create an array called $row for each record in the result set. To get the individual elements of the record (COFFEE_NAME, ROAST_TYPE, QUANTITY), create specific variables: 
$coffee_name = $row["COFFEE_NAME"];
$roast_type = $row["ROAST_TYPE"];
$quantity = $row["QUANTITY"];

You'll probably want to print the results in a simple HTML table. Step back and place this statement before the while loop begins, to open the table tag and create the row headings:
echo "";
echo "
      ";
After defining the variables within the while loop, print them in table format: 
echo "
      ";
The new while loop now looks like this:
while ($i < $num) {
	$row = pg_fetch_array($sql_result, $i);
	$coffee_name = $row["COFFEE_NAME"];
	$roast_type = $row["ROAST_TYPE"];
	$quantity = $row["QUANTITY"];
	echo "
	      ";
}

After the while loops, close the HTML table:

	
echo "

      
Coffee Name
      
Roast Type
      
Quantity
      


      
$coffee_name
      
$roast_type
      
$quantity
      


	      
$coffee_name
	      
$roast_type
	      
$quantity
	      
";

 
Finally, you'll want to free up the resources used to perform the query, and close the database connection. Failing to do so could cause memory leaks and other nasty resource-hogging things to occur. 
 
 
pg_freeresult($sql_result);
pg_close($connection);

?>

The full script to perform a simple connection and data selection from a PostgreSQL database could look something like this:
 
";
echo "