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Select, Insert, Update, and Delete Queries

You will routinely perform four types of queries when using any type of database. The insert query will place items in the database, the update query will update information that is already in the database, the select query will display information in the database, and the delete query will delete items from the database. When you query databases from inside PHP, you will allocate memory when a database connection is made and when the result set is returned from your query. When your script is finished executing, all memory will be freed, but it is good programming practice to free the result by using the pg_FreeResult() function and to close the connection by using the pg_Close() function.

Insert Queries

We will use the following example to insert information into our newly created database. This example consists of two parts. The first part is a simple form that enables the user to input specific information to be added to the database. This form calls the PHP script that takes the form variables, and then creates and executes the insert query. The HTML form looks like this:

<html>
<head>
<title>Insert Record</title>
</head>
<body>
  <b>Please provide us with the following:</b></font>
  <p><font size="2" face="Arial, Helvetica, sans-serif">
  <form action="insert.php" method="POST" enablecab="Yes">
   Full Name (Last, First MI):<br>
   <input type="Text" name="FullName" align="LEFT" required="Yes" 
    size="59" value=""><br>
   Address:<br>
   <input type="Text" name="Address" align="LEFT" required="Yes" 
    size="59" value=""><br>
   City:<br>
   <input type="Text" name="City" align="LEFT" required="Yes" 
    size="29" value=""><br>
   State:<br>
   <input type="Text" name="State" align="LEFT" required="Yes" 
    size="2" value=""><br>
   Zip:<br>
   <input type="Text" name="Zip" align="LEFT" required="Yes" 
    size="10" value=""><br>
   Phone:<br>
   <input type="Text" name="Phone" align="LEFT" required="No" 
    size="25" value=""><br>
   Fax:<br>
   <input type="Text" name="Fax" align="LEFT" required="Yes"
    size="25" value=""><br>
   Email:<br>
   <input type="Text" name="Email" align="LEFT" required="Yes" 
    size="59" value=""><br>
   <input type="Submit" name="Submit" value="Submit" align="MIDDLE">
  </form>
</body>
</html>

Notice that the form variables in the example are FullName, Address, City, State, Zip, Phone, Fax, and Email. The PHP script, which is named insert.php, refers to these posted form variables as $FirstName, $Address, $City, $State, $Zip, $Phone, $Fax, and $Email. The PHP script looks like this:

<html>
<head>
  <title>Insert the Form Data</title>
</head>
<body>
<?
// Connect to the Postgres Database
$conn = pg_Connect("localhost", "5432", "", "", "test");
 if (!$conn) {echo "An database connection error occurred.\n"; exit;}
// Insert the form values into the database
$result = pg_Exec($conn,"INSERT INTO contacts VALUES (NEXTVAL('c'),'$FullName',
'$Address','$City','$State','$Zip', '$Phone','$Fax','$Email');");
 if (!$result) {echo "An INSERT query error occurred.\n"; exit;}
// Get the last record inserted
$oid = pg_getlastoid($result);
 if (!$oid) {echo "An OID error occurred.\n"; exit;}
// Select the record that was last entered
$result = pg_Exec($conn,"SELECT cid FROM contacts WHERE oid=$oid;");
 if (!$result) {echo "A SELECT query error occurred.\n"; exit;}
// Place the result into the variable $CID
$CID = pg_Result($result, 0, "cid");
 if (!$CID) {echo "There is a problem returning the Contact ID.\n"; exit;}
// Print out the Contact ID
 else { echo "The record was successfully entered and the Contact ID is:
     $CID \n";}
// Free the result
pg_FreeResult($result);
// Close the connection
pg_Close($conn);
?>
</body>
</html>

The code for this example first inserts the information from the form into the database and then uses the pg_getlastoid() function to get the last record entered. It then uses the retrieved object identifier (OID) to query the database, and returns the customer identifier (CID) of the last record. If all goes well, the contact ID is printed to the browser window. The last part of this example is not needed to insert records using PHP, but it is included to illustrate the use of the pg_getlastoid() function.

Select Queries with PHP

We gave you a taste of a select query in the previous section. This section takes the result set from the select query and formats it for presentation in a Web page. The select query often displays information that you would like to either change or delete. Notice in the following example that edit and delete links are included. We will create these pages later in this chapter. For now, let's look at this example:

<html>
<head>
<title>Select Query</title>
<?
$conn = pg_Connect("localhost", "5432", "", "", "test");
  if (!$conn) {echo "An database connection error occurred.\n"; exit;}
$result = pg_Exec($conn,"SELECT cid, name, address, city, state, zip, phone,
          fax, email FROM contacts ORDER BY name");
  if (!$result) {echo "A query error occurred.\n"; exit;}
$ContactNum = pg_NumRows($result);
  $i = 0;
  while ($i < $ContactNum) {
   $CID[$i] = pg_Result($result, $i, "cid");
   $CName[$i] = pg_Result($result, $i, "name");
   $CAddress[$i] = pg_Result($result, $i, "address");
   $CCity[$i] = pg_Result($result, $i, "city");
   $CState[$i] = pg_Result($result, $i, "state");
   $CZip[$i] = pg_Result($result, $i, "zip");
   $CPhone[$i] = pg_Result($result, $i, "phone");
   $CFax[$i] = pg_Result($result, $i, "fax");
   $CEmail[$i] = pg_Result($result, $i, "email");
   $i++;
  }
pg_FreeResult($result);
pg_Close($conn);
?>
</head>
<body>
<table>
<TR>
  <TD></TD>
  <TD><b>Full Name</b></TD>
  <TD><b>Address</b></TD>
  <TD><b>City</b></TD>
  <TD><b>State</b></TD>
  <TD><b>Zip</b></TD>
  <TD><b>Phone</b></TD>
  <TD><b>Fax</b></TD>
  <TD><b>Email</b></TD>
</TR>
<?
  $i = 0;
  while ($i < $ContactNum) {
   echo "<TR><TD><A href=editform.php?ID=".$CID[$i].">[Edit]</A>";
   echo "<A href=delete.php?ID=".$CID[$i].">[Delete]</A></TD>";
   echo "<TD>".$CName[$i]."</TD>";
   echo "<TD>".$CAddress[$i]."</TD>";
   echo "<TD>".$CCity[$i]."</TD>";
   echo "<TD>".$CState[$i]."</TD>";
   echo "<TD>".$CZip[$i]."</TD>";
   echo "<TD>".$CPhone[$i]."</TD>";
   echo "<TD>".$CFax[$i]."</TD>";
   echo "<TD>".$CEmail[$i]."</TD></TR>";
  $i++;
}
?>
</table>
</body>
</html>

The next section examines this example and explains how to work with the data that is returned from the query.

Working with the Result Set

One of the main features of the preceding example is the use of an array to store the items that are returned from the select query. The while loop uses the pg_Result() function to get the records that are returned from the select query and stores them in variables. These variables are used later in the script to present the information to the Web browser. The pg_NumRows() function is used to return the number of returned records and, therefore, the number of times that the while loop should be executed to store all the returned information. Notice that a while loop is once again used to step through the array and print the variables in the appropriate place in an HTML table. The CID is used as an identifier in all the returned rows. After the edit and delete links are completed, this identifier will be used in subsequent queries to keep track of the record.

Update Queries

This section continues with the example that was started with the select query. After you click on the Edit hyperlink on the Select Query page, the CID is passed to the Edit Record page. The code listing for this page follows:

<html>
<head>
<title>Edit Record Form</title>
<?
$conn = pg_Connect("localhost", "5432", "", "", "test");
  if (!$conn) {echo "An database connection error occurred.\n"; exit;}
$result = pg_Exec($conn,"SELECT cid, name, address, city, state, zip, 
          phone, fax, email FROM contacts WHERE cid = $ID");
  if (!$result) {echo "A query error occurred.\n"; exit;}
 $CID = pg_Result($result, $i, "cid");
 $CName = pg_Result($result, $i, "name");
 $CAddress = pg_Result($result, $i, "address");
 $CCity = pg_Result($result, $i, "city");
 $CState = pg_Result($result, $i, "state");
 $CZip = pg_Result($result, $i, "zip");
 $CPhone = pg_Result($result, $i, "phone");
 $CFax = pg_Result($result, $i, "fax");
 $CEmail = pg_Result($result, $i, "email");
pg_FreeResult($result);
pg_Close($conn);
?><
</head>
<body>
  <b>Please update the following:</b></font>
  <p><font size="2" face="Arial, Helvetica, sans-serif">
  <form action="edit.php?ID=<? echo $CID ?>" method="POST" enablecab="Yes">
  Full Name (Last, First MI):<br>
  <input type="Text" name="FullName" align="LEFT" required="Yes" size="59" 
  value="<? echo $CName ?>"><br>
  Address:<br>
  <input type="Text" name="Address" align="LEFT" required="Yes" size="59"
  value="<? echo $CAddress ?>"><br>
  City:<br>
  <input type="Text" name="City" align="LEFT" required="Yes" size="29"
  value="<? echo $CCity ?>"><br>
  State:<br>
  <input type="Text" name="State" align="LEFT" required="Yes" size="2"
  value="<? echo $CState ?>"><br>
  Zip:<br>
  <input type="Text" name="Zip" align="LEFT" required="Yes" size="10"
  value="<? echo $CZip ?>"><br>
  Phone:<br>
  <input type="Text" name="Phone" align="LEFT" required="No" size="25"
  value="<? echo $CPhone ?>"><br>
  Fax:<br>
  <input type="Text" name="Fax" align="LEFT" required="Yes" size="25"
  value="<? echo $CFax ?>"><br>
  Email:<br>
  <input type="Text" name="Email" align="LEFT" required="Yes" size="59"
  value="<? echo $CEmail ?>"><br>
  <input type="Submit" name="Submit" value="Submit" align="MIDDLE">
  </form>
</body>
</html>

This script's first task is to determine, through the CID, which record is to be edited. This is done with a simple select query. The result set of this query is placed into variables to be used later in the HTML form. Notice that because only one record is to be returned, we do not need to use a while loop and an array to return multiple records. The returned variables are placed into the HTML input tag as the value of the field. This places the information in the input field and enables the end user to edit the information.

After the Submit button is pressed, the second part of this script performs the update query. The form variables are passed to this script and are used to create the update query that is sent to the database.

<html>
<head>
<title>Edit Record</title>
<?
$conn = pg_Connect("localhost", "5432", "", "", "test");
 if (!$conn) {echo "An database connection error occurred.\n"; exit;}
$result = pg_Exec($conn,"UPDATE contacts SET name='$FullName',
     address='$Address', city='$City', state='$State', zip='$Zip',
     phone='$Phone', fax='$Fax', email='$Email' WHERE cid='$ID'");
 if (!$result) {echo "An UPDATE query error occurred.\n"; exit;}
$result = pg_Exec($conn,"SELECT cid, name, address, city, state, zip,
     phone, fax, email FROM contacts WHERE cid=$ID;");
 if (!$result) {echo "A query error occurred.\n"; exit;}
 $CID = pg_Result($result, $i, "cid");
 $CName = pg_Result($result, $i, "name");<
 $CAddress = pg_Result($result, $i, "address");
 $CCity = pg_Result($result, $i, "city");
 $CState = pg_Result($result, $i, "state");
 $CZip = pg_Result($result, $i, "zip");
 $CPhone = pg_Result($result, $i, "phone");
 $CFax = pg_Result($result, $i, "fax");
 $CEmail = pg_Result($result, $i, "email");
pg_FreeResult($result);
pg_Close($conn); 
?>
</head>
<body>
<b>The information has been changed to:</b><br>
  Full Name (Last, First MI):<br>
  <b><? echo $CName ?></b><br>
  Address:<br>
  <b><? echo $CAddress ?></b><br>
  City:<br>
  <b><? echo $CCity ?></b><br>
  State:<br>
  <b><? echo $CState ?></b><br>
  Zip:<br>
  <b><? echo $CZip ?></b><br>
  Phone:<br>
  <b><? echo $CPhone ?></b><br>
  Fax:<br>
  <b><? echo $CFax ?></b><br>
  Email:<br>
  <b><? echo $CEmail ?></b><br><br>
<a href=select.php>Back to Select Page</a>
</body>
</html>

Notice that this script verifies that information in the database was changed by performing a select query, which displays the changed information in the browser window.

Delete Queries

The delete query is the last of our simple examples. If the delete link is clicked from the initial select query page, the CID ID is passed to the following script:

<title>Delete Record</title>
<?
$conn = pg_Connect("localhost", "5432", "", "", "test");
 if (!$conn) {echo "An database connection error occurred.\n"; exit;}
$result = pg_Exec($conn,"DELETE FROM contacts WHERE cid='$ID'");
 if (!$result) {echo "A DELETE query error occurred.\n"; exit;}
pg_FreeResult($result);
pg_Close($conn);
?>
</head>
<body>
<b>The record was deleted</b><br><br>
<a href=select.php>Back to Select Page</a>
</body>
</html>

This script simply deletes the record defined by the CID from the database. You can click the Back to Select Page link to verify that the record was deleted.

This concludes the four functions that all database applications perform. We illustrated how PHP accomplishes insert, select, update, and delete queries using PostgreSQL as the database. We also gave some examples of how to use PHP to display and manipulate the information in the Web browser.

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