sqlsrv_field_metadata

Artikel
11/18/2022

Retrieves metadata for the fields of a prepared statement. For information about preparing a statement, see sqlsrv_query or sqlsrv_prepare. Note that sqlsrv_field_metadata can be called on any prepared statement, pre- or post-execution.

Syntax

  
sqlsrv_field_metadata( resource $stmt)

Parameters

$stmt: A statement resource for which field metadata is sought.

Return Value

An array of arrays or false. The array consists of one array for each field in the result set. Each sub-array has keys as described in the table below. If there is an error in retrieving field metadata, false is returned.

Key	Description
Name	Name of the column to which the field corresponds.
Type	Numeric value that corresponds to a SQL type.
Size	Number of characters for fields of character type (char(n), varchar(n), nchar(n), nvarchar(n), XML). Number of bytes for fields of binary type (binary(n), varbinary(n), UDT). NULL for other SQL Server data types.
Precision	The precision for types of variable precision (real, numeric, decimal, datetime2, datetimeoffset, and time). NULL for other SQL Server data types.
Scale	The scale for types of variable scale (numeric, decimal, datetime2, datetimeoffset, and time). NULL for other SQL Server data types.
Nullable	An enumerated value indicating whether the column is nullable (SQLSRV_NULLABLE_YES), the column is not nullable (SQLSRV_NULLABLE_NO), or it is not known if the column is nullable (SQLSRV_NULLABLE_UNKNOWN).

The following table gives more information on the keys for each sub-array (see the SQL Server documentation for more information on these types):

SQL Server 2008 data type	Type	Min/Max Precision	Min/Max Scale	Size
bigint	SQL_BIGINT (-5)			8
binary	SQL_BINARY (-2)			0 < n < 8000 ¹
bit	SQL_BIT (-7)
char	SQL_CHAR (1)			0 < n < 8000 ¹
date	SQL_TYPE_DATE (91)	10/10	0/0
datetime	SQL_TYPE_TIMESTAMP (93)	23/23	3/3
datetime2	SQL_TYPE_TIMESTAMP (93)	19/27	0/7
datetimeoffset	SQL_SS_TIMESTAMPOFFSET (-155)	26/34	0/7
decimal	SQL_DECIMAL (3)	1/38	0/precision value
float	SQL_FLOAT (6)	4/8
image	SQL_LONGVARBINARY (-4)			2 GB
int	SQL_INTEGER (4)
money	SQL_DECIMAL (3)	19/19	4/4
nchar	SQL_WCHAR (-8)			0 < n < 4000 ¹
ntext	SQL_WLONGVARCHAR (-10)			1 GB
numeric	SQL_NUMERIC (2)	1/38	0/precision value
nvarchar	SQL_WVARCHAR (-9)			0 < n < 4000 ¹
real	SQL_REAL (7)	4/4
smalldatetime	SQL_TYPE_TIMESTAMP (93)	16/16	0/0
smallint	SQL_SMALLINT (5)			2 bytes
Smallmoney	SQL_DECIMAL (3)	10/10	4/4
sql_variant	SQL_SS_VARIANT (-150)			variable
text	SQL_LONGVARCHAR (-1)			2 GB
time	SQL_SS_TIME2 (-154)	8/16	0/7
timestamp	SQL_BINARY (-2)			8 bytes
tinyint	SQL_TINYINT (-6)			1 byte
udt	SQL_SS_UDT (-151)			variable
uniqueidentifier	SQL_GUID (-11)			16
varbinary	SQL_VARBINARY (-3)			0 < n < 8000 ¹
varchar	SQL_VARCHAR (12)			0 < n < 8000 ¹
xml	SQL_SS_XML (-152)			0

(1) Zero (0) indicates that the maximum size is allowed.

The Nullable key can either be yes or no.

Example

The following example creates a statement resource, then retrieves and displays the field metadata. The example assumes that SQL Server and the AdventureWorks database are installed on the local computer. All output is written to the console when the example is run from the command line.

<?php
/* Connect to the local server using Windows Authentication and
specify the AdventureWorks database as the database in use. */
$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));
}

/* Prepare the statement. */
$tsql = "SELECT ReviewerName, Comments FROM Production.ProductReview";
$stmt = sqlsrv_prepare( $conn, $tsql);
  
/* Get and display field metadata. */
foreach( sqlsrv_field_metadata( $stmt) as $fieldMetadata) {
    foreach( $fieldMetadata as $name => $value) {
        echo "$name: $value\n";
    }  
    echo "\n";
}  
  
/* Note: sqlsrv_field_metadata can be called on any statement
resource, pre- or post-execution. */
  
/* Free statement and connection resources. */
sqlsrv_free_stmt($stmt);
sqlsrv_close($conn);
?>

Sensitivity Data Classification Metadata

A new option DataClassification is introduced in version 5.8.0 for users to access the sensitivity data classification metadata in Microsoft SQL Server 2019 using sqlsrv_field_metadata, which requires Microsoft ODBC Driver 17.4.2 or above.

By default, the option DataClassification is false, but when set to true, the array returned by sqlsrv_field_metadata will be populated with the sensitivity data classification metadata, if it exists.

Take a Patients table for example:

CREATE TABLE Patients 
      [PatientId] int identity,
      [SSN] char(11),
      [FirstName] nvarchar(50),
      [LastName] nvarchar(50),
      [BirthDate] date)

We can classify the SSN and BirthDate columns as shown below:

ADD SENSITIVITY CLASSIFICATION TO [Patients].SSN WITH (LABEL = 'Highly Confidential - secure privacy', INFORMATION_TYPE = 'Credentials')
ADD SENSITIVITY CLASSIFICATION TO [Patients].BirthDate WITH (LABEL = 'Confidential Personal Data', INFORMATION_TYPE = 'Birthdays')

To access the metadata, invoke sqlsrv_field_metadata as shown in the snippet below:

$tableName = 'Patients';
$tsql = "SELECT * FROM $tableName";
$stmt = sqlsrv_prepare($conn, $tsql, array(), array('DataClassification' => true));
if (sqlsrv_execute($stmt)) {
    $fieldmeta = sqlsrv_field_metadata($stmt);

    foreach ($fieldmeta as $f) {
        if (count($f['Data Classification']) > 0) {
            echo $f['Name'] . ": \n";
            print_r($f['Data Classification']); 
        }
    }
}

The output will be:

SSN: 
Array
(
    [0] => Array
        (
            [Label] => Array
                (
                    [name] => Highly Confidential - secure privacy
                    [id] => 
                )

            [Information Type] => Array
                (
                    [name] => Credentials
                    [id] => 
                )

        )

)
BirthDate: 
Array
(
    [0] => Array
        (
            [Label] => Array
                (
                    [name] => Confidential Personal Data
                    [id] => 
                )

            [Information Type] => Array
                (
                    [name] => Birthdays
                    [id] => 
                )

        )

)

If using sqlsrv_query instead of sqlsrv_prepare, the above snippet can be modified, like this:

$tableName = 'Patients';
$tsql = "SELECT * FROM $tableName";
$stmt = sqlsrv_query($conn, $tsql, array(), array('DataClassification' => true));
$fieldmeta = sqlsrv_field_metadata($stmt);

foreach ($fieldmeta as $f) {
    $jstr = json_encode($f);
    echo $jstr . PHP_EOL;
}

As you can see in the JSON representation below, the data classification metadata is shown if associated with the columns:

{"Name":"PatientId","Type":4,"Size":null,"Precision":10,"Scale":null,"Nullable":0,"Data Classification":[]}
{"Name":"SSN","Type":1,"Size":11,"Precision":null,"Scale":null,"Nullable":1,"Data Classification":[{"Label":{"name":"Highly Confidential - secure privacy","id":""},"Information Type":{"name":"Credentials","id":""}}]}
{"Name":"FirstName","Type":-9,"Size":50,"Precision":null,"Scale":null,"Nullable":1,"Data Classification":[]}
{"Name":"LastName","Type":-9,"Size":50,"Precision":null,"Scale":null,"Nullable":1,"Data Classification":[]}
{"Name":"BirthDate","Type":91,"Size":null,"Precision":10,"Scale":0,"Nullable":1,"Data Classification":[{"Label":{"name":"Confidential Personal Data","id":""},"Information Type":{"name":"Birthdays","id":""}}]}

Sensitivity Rank using a predefined set of values

Beginning with 5.9.0, PHP drivers added classification rank retrieval when using ODBC Driver 17.4.2 or above. The user may define rank when using ADD SENSITIVITY CLASSIFICATION to classify any data column.

For example, if the user assigns NONE and LOW to BirthDate and SSN respectively, the JSON representation is shown as follows:

{"0":{"Label":{"name":"Confidential Personal Data","id":""},"Information Type":{"name":"Birthdays","id":""},"rank":0},"rank":0}
{"0":{"Label":{"name":"Highly Confidential - secure privacy","id":""},"Information Type":{"name":"Credentials","id":""},"rank":10},"rank":10}

As shown in sensitivity classification, the numerical values of the ranks are:

0 for NONE
10 for LOW
20 for MEDIUM
30 for HIGH
40 for CRITICAL

Hence, if instead of RANK=NONE, the user defines RANK=CRITICAL when classifying the column BirthDate, the classification metadata will be:

  array(7) {
    ["Name"]=>
    string(9) "BirthDate"
    ["Type"]=>
    int(91)
    ["Size"]=>
    NULL
    ["Precision"]=>
    int(10)
    ["Scale"]=>
    int(0)
    ["Nullable"]=>
    int(1)
    ["Data Classification"]=>
    array(2) {
      [0]=>
      array(3) {
        ["Label"]=>
        array(2) {
          ["name"]=>
          string(26) "Confidential Personal Data"
          ["id"]=>
          string(0) ""
        }
        ["Information Type"]=>
        array(2) {
          ["name"]=>
          string(9) "Birthdays"
          ["id"]=>
          string(0) ""
        }
        ["rank"]=>
        int(40)
      }
      ["rank"]=>
      int(40)
    }
  }

The updated JSON representation is shown below:

{"0":{"Label":{"name":"Confidential Personal Data","id":""},"Information Type":{"name":"Birthdays","id":""},"rank":40},"rank":40}

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