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WordPress provides a class of functions for all database manipulations. The class is called wpdb and is loosely based on the ezSQL class written and maintained by Justin Vincent.
Methods in the wpdb() class should not be called directly.
WordPress provides a global variable, $wpdb, which is an instantiation of the class already set up to talk to the WordPress database. Always use the global $wpdb variable. (Remember to globalize $wpdb before using it in any custom functions.)
The $wpdb object can be used to read data from any table in the WordPress database (such as custom plugin tables), not just the standard tables that WordPress creates. For example to SELECT some information from a custom table called "mytable", you can do the following.
$myrows = $wpdb->get_results( "SELECT id, name FROM mytable" );
The $wpdb object can talk to any number of tables, but only one database: the WordPress database. In the rare case you need to connect to another database, you will have to instantiate your own object from the wpdb class with the appropriate connection details. For extremely complicated setups with many databases, consider using hyperdb instead.
The query function allows you to execute any SQL query on the WordPress database. It is best to use a more specific function (see below), however, for SELECT queries.
<?php $wpdb->query('query'); ?>
The function returns an integer corresponding to the number of rows affected/selected. If there is a MySQL error, the function will return FALSE. (Note: since both 0 and FALSE can be returned, make sure you use the correct comparison operator: equality == vs. identicality ===).
Note: As with all functions in this class that execute SQL queries, you must SQL escape all inputs (e.g., wpdb->escape($user_entered_data_string)). See the section entitled Protect Queries Against SQL Injection Attacks below.
Delete the 'gargle' meta key and value from Post 13. (We'll add the 'prepare' method to make sure we're not dealing with an illegal operation or any illegal characters):
$wpdb->query(
$wpdb->prepare(
"
DELETE FROM $wpdb->postmeta
WHERE post_id = %d
AND meta_key = %s
",
13, 'gargle'
)
);
Performed in WordPress by delete_post_meta().
Set the parent of Page 15 to Page 7.
$wpdb->query( " UPDATE $wpdb->posts SET post_parent = 7 WHERE ID = 15 AND post_status = 'static' " );
The get_var function returns a single variable from the database. Though only one variable is returned, the entire result of the query is cached for later use. Returns NULL if no result is found.
<?php $wpdb->get_var('query',column_offset,row_offset); ?>
null will return the specified variable from the cached results of the previous query.
Retrieve and display the number of users.
<?php
$user_count = $wpdb->get_var( "SELECT COUNT(*) FROM $wpdb->users" );
echo "<p>User count is {$user_count}</p>";
?>
Retrieve and display the sum of a Custom Field value.
<?php
// set the meta_key to the appropriate custom field meta key
$meta_key = 'miles';
$allmiles = $wpdb->get_var( $wpdb->prepare(
"
SELECT sum(meta_value)
FROM $wpdb->postmeta
WHERE meta_key = %s
",
$meta_key
) );
echo "<p>Total miles is {$allmiles}</p>";
?>
To retrieve an entire row from a query, use get_row. The function can return the row as an object, an associative array, or as a numerically indexed array. If more than one row is returned by the query, only the specified row is returned by the function, but all rows are cached for later use. Returns NULL if no result is found, consider this when using the returned value in arguments, see example below.
<?php $wpdb->get_row('query', output_type, row_offset); ?>
Get all the information about Link 10.
$mylink = $wpdb->get_row("SELECT * FROM $wpdb->links WHERE link_id = 10");
The properties of the $mylink object are the column names of the result from the SQL query (in this example all the columns from the $wpdb->links table, but you could also query for specific columns only).
echo $mylink->link_id; // prints "10"
In contrast, using
$mylink = $wpdb->get_row("SELECT * FROM $wpdb->links WHERE link_id = 10", ARRAY_A);
would result in an associative array:
echo $mylink['link_id']; // prints "10"
and
$mylink = $wpdb->get_row("SELECT * FROM $wpdb->links WHERE link_id = 10", ARRAY_N);
would result in a numerically indexed array:
echo $mylink[1]; // prints "10"
If there is no record with ID 10 in the links table, null will be returned. The following would then be false:
if ($mylink != null) {
// do something with the link
return true;
} else {
// no link found
return false;
}
To SELECT a column, use get_col. This function outputs a one dimensional array. If more than one column is returned by the query, only the specified column will be returned by the function, but the entire result is cached for later use. Returns an empty array if no result is found.
<?php $wpdb->get_col( 'query', column_offset ); ?>
null will return the specified column from the cached results of the previous query.
For this example, assume the blog is devoted to information about automobiles. Each post describes a particular car (e.g. 1969 Ford Mustang), and three Custom Fields, manufacturer, model, and year, are assigned to each post. This example will display the post titles, filtered by a particular manufacturer (Ford), and sorted by model and year.
The get_col form of the wpdb Class is used to return an array of all the post ids meeting the criteria and sorted in the correct order. Then a foreach construct is used to iterate through that array of post ids, displaying the title of each post. Note that the SQL for this example was created by Andomar.
<?php
$meta_key1 = 'model';
$meta_key2 = 'year';
$meta_key3 = 'manufacturer';
$meta_key3_value = 'Ford';
$postids=$wpdb->get_col( $wpdb->prepare(
"
SELECT key3.post_id
FROM $wpdb->postmeta key3
INNER JOIN $wpdb->postmeta key1
ON key1.post_id = key3.post_id
AND key1.meta_key = %s
INNER JOIN $wpdb->postmeta key2
ON key2.post_id = key3.post_id
AND key2.meta_key = %s
WHERE key3.meta_key = %s
AND key3.meta_value = %s
ORDER BY key1.meta_value, key2.meta_value
",
$meta_key1,
$meta_key2,
$meta_key3,
$meta_key3_value
) );
if ( $postids )
{
echo "List of {$meta_key3_value}(s), sorted by {$meta_key1}, {$meta_key2}";
foreach ( $postids as $id )
{
$post = get_post( intval( $id ) );
setup_postdata( $post );
?>
<p>
<a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>">
<?php the_title(); ?>
</a>
</p>
<?php
}
}
?>
This example lists all posts that contain a particular custom field, but sorted by the value of a second custom field.
<?php
// List all posts with custom field Color, sorted by the value of custom field Display_Order
// does not exclude any 'post_type'
// assumes each post has just one custom field for Color, and one for Display_Order
$meta_key1 = 'Color';
$meta_key2 = 'Display_Order';
$postids = $wpdb->get_col( $wpdb->prepare(
"
SELECT key1.post_id
FROM $wpdb->postmeta key1
INNER JOIN $wpdb->postmeta key2
ON key2.post_id = key1.post_id
AND key2.meta_key = %s
WHERE key1.meta_key = %s
ORDER BY key2.meta_value+(0) ASC
",
$meta_key2,
$meta_key1
) );
if ( $postids )
{
echo "List of {$meta_key1} posts, sorted by {$meta_key2}";
foreach ( $postids as $id )
{
$post = get_post( intval( $id ) );
setup_postdata( $post );
?>
<p>
<a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>">
<?php the_title(); ?>
</a>
</p>
<?php
}
}
?>
Generic, mulitple row results can be pulled from the database with get_results. The function returns the entire query result as an array, or NULL on no result. Each element of this array corresponds to one row of the query result and, like get_row, can be an object, an associative array, or a numbered array.
<?php $wpdb->get_results('query', output_type); ?>
null will return the data from the cached results of the previous query.
Since this function uses the '$wpdb->query()' function all the class variables are properly set. The results count for a 'SELECT' query will be stored in $wpdb->num_rows.
Get the IDs and Titles of all the Drafts by User 5 and echo the Titles.
$fivesdrafts = $wpdb->get_results(
"
SELECT ID, post_title
FROM $wpdb->posts
WHERE post_status = 'draft'
AND post_author = 5
"
);
foreach ( $fivesdrafts as $fivesdraft )
{
echo $fivesdraft->post_title;
}
Get all information on the Drafts by User 5.
<?php
$fivesdrafts = $wpdb->get_results(
"
SELECT *
FROM $wpdb->posts
WHERE post_status = 'draft'
AND post_author = 5
"
);
if ( $fivesdrafts )
{
foreach ( $fivesdrafts as $post )
{
setup_postdata( $post );
?>
<h2>
<a href="<?php the_permalink(); ?>" rel="bookmark" title="Permalink: <?php the_title(); ?>">
<?php the_title(); ?>
</a>
</h2>
<?php
}
}
else
{
?>
<h2>Not Found</h2>
<?php
}
?>
Insert a row into a table.
<?php $wpdb->insert( $table, $data, $format ); ?>
Possible format values: %s as string; %d as decimal number; and %f as float.
After insert, the ID generated for the AUTO_INCREMENT column can be accessed with:
$wpdb->insert_id
This function returns false if the row could not be inserted.
Insert two columns in a row, the first value being a string and the second a number:
$wpdb->insert( 'table', array( 'column1' => 'value1', 'column2' => 123 ), array( '%s', '%d' ) );
Update a row in the table. Returns false if errors, or the number of rows affected if successful.
<?php $wpdb->update( $table, $data, $where, $format = null, $where_format = null ); ?>
Possible format values: %s as string; %d as decimal number and %f as float. If omitted, all values in $where will be treated as strings.
This function returns the number of rows updated, or false if there is an error.
Update a row, where the ID is 1, the value in the first column is a string and the value in the second column is a number:
$wpdb->update( 'table', array( 'column1' => 'value1', // string 'column2' => 'value2' // integer (number) ), array( 'ID' => 1 ), array( '%s', // value1 '%d' // value2 ), array( '%d' ) );
Attention: %d can't deal with comma values - if you're not using full numbers, use string/%s.
For a more complete overview of SQL escaping in WordPress, see database Data Validation. That Data Validation article is a must-read for all WordPress code contributors and plugin authors.
Briefly, though, all data in SQL queries must be SQL-escaped before the SQL query is executed to prevent against SQL injection attacks. This can be conveniently done with the prepare method, which supports both a sprintf()-like and vsprintf()-like syntax.
Please note: As of 3.5, wpdb::prepare() enforces a minimum of 2 arguments. [more info]
<?php $sql = $wpdb->prepare( 'query' , value_parameter[, value_parameter ... ] ); ?>
%s and %d placeholders. Any other % characters may cause parsing errors unless they are escaped. All % characters inside SQL string literals, including LIKE wildcards, must be double-% escaped as %%.
Add Meta key => value pair "Harriet's Adages" => "WordPress' database interface is like Sunday Morning: Easy." to Post 10.
$metakey = "Harriet's Adages";
$metavalue = "WordPress' database interface is like Sunday Morning: Easy.";
$wpdb->query( $wpdb->prepare(
"
INSERT INTO $wpdb->postmeta
( post_id, meta_key, meta_value )
VALUES ( %d, %s, %s )
",
10,
$metakey,
$metavalue
) );
Performed in WordPress by add_meta().
The same query using vsprintf()-like syntax.
$metakey = "Harriet's Adages";
$metavalue = "WordPress' database interface is like Sunday Morning: Easy.";
$wpdb->query( $wpdb->prepare(
"
INSERT INTO $wpdb->postmeta
( post_id, meta_key, meta_value )
VALUES ( %d, %s, %s )
",
array(
10,
$metakey,
$metavalue
)
) );
Note that in this example we pack the values together in an array. This can be useful when we don't know the number of arguments we need to pass until runtime.
Notice that you do not have to worry about quoting strings. Instead of passing the variables directly into the SQL query, use a %s placeholder for strings and a %d placedolder for integers. You can pass as many values as you like, each as a new parameter in the prepare() method.
Attention: You can't pass integers/numbers that have comma values via %d. If you need comma values, use %s instead.
You can turn error echoing on and off with the show_errors and hide_errors, respectively.
<?php $wpdb->show_errors(); ?>
<?php $wpdb->hide_errors(); ?>
You can also print the error (if any) generated by the most recent query with print_error.
<?php $wpdb->print_error(); ?>
Note: If you are running WordPress Multisite, you must define the DIEONDBERROR constant for database errors to display like so:
<?php define( 'DIEONDBERROR', true ); ?>
You can retrieve information about the columns of the most recent query result with get_col_info. This can be useful when a function has returned an OBJECT whose properties you don't know. The function will output the desired information from the specified column, or an array with information on all columns from the query result if no column is specified.
<?php $wpdb->get_col_info('type', offset); ?>
You can clear the SQL result cache with flush.
<?php $wpdb->flush(); ?>
This clears $wpdb->last_result, $wpdb->last_query, and $wpdb->col_info.
If you are using Multi-Site, you also have access to the following:
The WordPress database tables are easily referenced in the wpdb class.
These tables are used only in multisite installations.
wpdb() is located in wp-includes/wp-db.php.
