Cursor Types (SQLSRV Driver)

Artikel
11/18/2022

The SQLSRV driver lets you create a result set with rows that you can access in any order, depending on the cursor type. This topic will discuss client-side (buffered) and server-side (unbuffered) cursors.

Cursor Types

When you create a result set with sqlsrv_query or with sqlsrv_prepare, you can specify the type of cursor. By default, a forward-only cursor is used, which lets you move one row at a time starting at the first row of the result set until you reach the end of the result set.

You can create a result set with a scrollable cursor, which allows you to access any row in the result set, in any order. The following table lists the values that can be passed to the Scrollable option in sqlsrv_query or sqlsrv_prepare.

Option	Description
SQLSRV_CURSOR_FORWARD	Lets you move one row at a time starting at the first row of the result set until you reach the end of the result set. This is the default cursor type. sqlsrv_num_rows returns an error for result sets created with this cursor type. forward is the abbreviated form of SQLSRV_CURSOR_FORWARD.
SQLSRV_CURSOR_STATIC	Lets you access rows in any order but will not reflect changes in the database. static is the abbreviated form of SQLSRV_CURSOR_STATIC.
SQLSRV_CURSOR_DYNAMIC	Lets you access rows in any order and will reflect changes in the database. sqlsrv_num_rows returns an error for result sets created with this cursor type. dynamic is the abbreviated form of SQLSRV_CURSOR_DYNAMIC.
SQLSRV_CURSOR_KEYSET	Lets you access rows in any order. However, a keyset cursor does not update the row count if a row is deleted from the table (a deleted row is returned with no values). keyset is the abbreviated form of SQLSRV_CURSOR_KEYSET.
SQLSRV_CURSOR_CLIENT_BUFFERED	Lets you access rows in any order. Creates a client-side cursor query. buffered is the abbreviated form of SQLSRV_CURSOR_CLIENT_BUFFERED.

If a query generates multiple result sets, the Scrollable option applies to all result sets.

Selecting Rows in a Result Set

After you create a result set, you can use sqlsrv_fetch, sqlsrv_fetch_array, or sqlsrv_fetch_object to specify a row.

The following table describes the values you can specify in the row parameter.

Parameter	Description
SQLSRV_SCROLL_NEXT	Specifies the next row. This is the default value, if you do not specify the row parameter for a scrollable result set.
SQLSRV_SCROLL_PRIOR	Specifies the row before the current row.
SQLSRV_SCROLL_FIRST	Specifies the first row in the result set.
SQLSRV_SCROLL_LAST	Specifies the last row in the result set.
SQLSRV_SCROLL_ABSOLUTE	Specifies the row specified with the offset parameter.
SQLSRV_SCROLL_RELATIVE	Specifies the row specified with the offset parameter from the current row.

Server-Side Cursors and the SQLSRV Driver

The following example shows the effect of the various cursors. On line 33 of the example, you see the first of three query statements that specify different cursors. Two of the query statements are commented. Each time you run the program, use a different cursor type to see the effect of the database update on line 47.

<?php  
$server = "server_name";  
$conn = sqlsrv_connect( $server, array( 'Database' => 'test' ));  
if ( $conn === false ) {  
   die( print_r( sqlsrv_errors(), true ));  
}  
  
$stmt = sqlsrv_query( $conn, "DROP TABLE dbo.ScrollTest" );  
if ( $stmt !== false ) {   
   sqlsrv_free_stmt( $stmt );   
}  
  
$stmt = sqlsrv_query( $conn, "CREATE TABLE ScrollTest (id int, value char(10))" );  
if ( $stmt === false ) {  
   die( print_r( sqlsrv_errors(), true ));  
}  
  
$stmt = sqlsrv_query( $conn, "INSERT INTO ScrollTest (id, value) VALUES(?,?)", array( 1, "Row 1" ));  
if ( $stmt === false ) {  
   die( print_r( sqlsrv_errors(), true ));  
}  
  
$stmt = sqlsrv_query( $conn, "INSERT INTO ScrollTest (id, value) VALUES(?,?)", array( 2, "Row 2" ));  
if ( $stmt === false ) {  
   die( print_r( sqlsrv_errors(), true ));  
}  
  
$stmt = sqlsrv_query( $conn, "INSERT INTO ScrollTest (id, value) VALUES(?,?)", array( 3, "Row 3" ));  
if ( $stmt === false ) {  
   die( print_r( sqlsrv_errors(), true ));  
}  
  
$stmt = sqlsrv_query( $conn, "SELECT * FROM ScrollTest", array(), array( "Scrollable" => 'keyset' ));  
// $stmt = sqlsrv_query( $conn, "SELECT * FROM ScrollTest", array(), array( "Scrollable" => 'dynamic' ));  
// $stmt = sqlsrv_query( $conn, "SELECT * FROM ScrollTest", array(), array( "Scrollable" => 'static' ));  
  
$rows = sqlsrv_has_rows( $stmt );  
if ( $rows != true ) {  
   die( "Should have rows" );  
}  
  
$result = sqlsrv_fetch( $stmt, SQLSRV_SCROLL_LAST );  
$field1 = sqlsrv_get_field( $stmt, 0 );  
$field2 = sqlsrv_get_field( $stmt, 1 );  
echo "\n$field1 $field2\n";  
  
$stmt2 = sqlsrv_query( $conn, "delete from ScrollTest where id = 3" );  
// or  
// $stmt2 = sqlsrv_query( $conn, "UPDATE ScrollTest SET id = 4 WHERE id = 3" );  
if ( $stmt2 !== false ) {   
   sqlsrv_free_stmt( $stmt2 );   
}  
  
$result = sqlsrv_fetch( $stmt, SQLSRV_SCROLL_LAST );  
$field1 = sqlsrv_get_field( $stmt, 0 );  
$field2 = sqlsrv_get_field( $stmt, 1 );  
echo "\n$field1 $field2\n";  
  
sqlsrv_free_stmt( $stmt );  
sqlsrv_close( $conn );  
?>

Client-Side Cursors and the SQLSRV Driver

Client-side cursors are a feature added in version 3.0 of the Microsoft Drivers for PHP for SQL Server that allows you to cache an entire result set in memory. Row count is available after the query is executed when using a client-side cursor.

Client-side cursors should be used for small- to medium-sized result sets. Use server-side cursors for large result sets.

A query will return false if the buffer is not large enough to hold the entire result set. You can increase the buffer size up to the PHP memory limit.

Using the SQLSRV driver, you can configure the size of the buffer that holds the result set with the ClientBufferMaxKBSize setting for sqlsrv_configure. sqlsrv_get_config returns the value of ClientBufferMaxKBSize. You can also set the maximum buffer size in the php.ini file with sqlsrv.ClientBufferMaxKBSize (for example, sqlsrv.ClientBufferMaxKBSize = 1024).

The following sample shows:

Row count is always available with a client-side cursor.
Use of client-side cursors and batch statements.

<?php  
$serverName = "(local)";  
$connectionInfo = array("Database"=>"AdventureWorks");  
$conn = sqlsrv_connect( $serverName, $connectionInfo);  
  
if ( $conn === false ) {  
   echo "Could not connect.\n";  
   die( print_r( sqlsrv_errors(), true));  
}  
  
$tsql = "select * from HumanResources.Department";  
  
// Execute the query with client-side cursor.  
$stmt = sqlsrv_query($conn, $tsql, array(), array("Scrollable"=>"buffered"));  
if (! $stmt) {  
   echo "Error in statement execution.\n";  
   die( print_r( sqlsrv_errors(), true));  
}  
  
// row count is always available with a client-side cursor  
$row_count = sqlsrv_num_rows( $stmt );  
echo "\nRow count = $row_count\n";  
  
// Move to a specific row in the result set.  
$row = sqlsrv_fetch($stmt, SQLSRV_SCROLL_FIRST);  
$EmployeeID = sqlsrv_get_field( $stmt, 0);  
echo "Employee ID = $EmployeeID \n";  
  
// Client-side cursor and batch statements  
$tsql = "select top 2 * from HumanResources.Employee;Select top 3 * from HumanResources.EmployeeAddress";  
  
$stmt = sqlsrv_query($conn, $tsql, array(), array("Scrollable"=>"buffered"));  
if (! $stmt) {  
   echo "Error in statement execution.\n";  
   die( print_r( sqlsrv_errors(), true));  
}  
  
$row_count = sqlsrv_num_rows( $stmt );  
echo "\nRow count for first result set = $row_count\n";  
  
$row = sqlsrv_fetch($stmt, SQLSRV_SCROLL_FIRST);  
$EmployeeID = sqlsrv_get_field( $stmt, 0);  
echo "Employee ID = $EmployeeID \n";  
  
sqlsrv_next_result($stmt);  
  
$row_count = sqlsrv_num_rows( $stmt );  
echo "\nRow count for second result set = $row_count\n";  
  
$row = sqlsrv_fetch($stmt, SQLSRV_SCROLL_LAST);  
$EmployeeID = sqlsrv_get_field( $stmt, 0);  
echo "Employee ID = $EmployeeID \n";  
?>

The following sample shows a client-side cursor using sqlsrv_prepare and a different client buffer size.

<?php  
$serverName = "(local)";  
$connectionInfo = array( "Database"=>"AdventureWorks");  
$conn = sqlsrv_connect( $serverName, $connectionInfo);  
  
if ( $conn === false ) {  
   echo "Could not connect.\n";  
   die( print_r( sqlsrv_errors(), true));  
}  
  
$tsql = "select * from HumanResources.Employee";  
$stmt = sqlsrv_prepare( $conn, $tsql, array(), array("Scrollable" => SQLSRV_CURSOR_CLIENT_BUFFERED, "ClientBufferMaxKBSize" => 51200));
  
if (! $stmt ) {  
   echo "Statement could not be prepared.\n";  
   die( print_r( sqlsrv_errors(), true));  
}  
  
sqlsrv_execute( $stmt);  
  
$row_count = sqlsrv_num_rows( $stmt );  
if ($row_count)  
   echo "\nRow count = $row_count\n";  
  
$row = sqlsrv_fetch($stmt, SQLSRV_SCROLL_FIRST);  
if ($row ) {  
   $EmployeeID = sqlsrv_get_field( $stmt, 0);  
   echo "Employee ID = $EmployeeID \n";  
}  
?>

Dela via

Cursor Types (SQLSRV Driver)

Cursor Types

Selecting Rows in a Result Set

Server-Side Cursors and the SQLSRV Driver

Client-Side Cursors and the SQLSRV Driver

See Also

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