How to Retrieve Specific Fields from the Database using wpdb in WordPress Plugin
Posted on 17th June 2023
Introduction
In WordPress plugin development, it is often necessary to retrieve specific fields from the database. The WordPress database class, wpdb, provides a simple interface for accessing data in the WordPress database. In this article, we will show you how to use wpdb to retrieve specific fields from the database.
Using wpdb to Retrieve Fields from the Database
The WordPress database class, wpdb, provides a simple interface for accessing data in the WordPress database. To use wpdb, you first need to include the class in your plugin file:
require_once( ABSPATH . 'wp-admin/includes/upgrade.php' );
global $wpdb;
You can then use the $wpdb object to run SQL queries on the WordPress database. For example, the following code would retrieve all posts from the database:
$posts = $wpdb->get_results( "SELECT * FROM $wpdb->posts" );
If you only want to retrieve specific fields from the database, you can use the $wpdb->get_results() method to specify the fields you want to retrieve. For example, the following code would retrieve the post title and content for all posts in the database:
$posts = $wpdb->get_results( "SELECT post_title, post_content FROM $wpdb->posts" );
You can also use the $wpdb->get_var() method to retrieve a single value from the database. For example, the following code would retrieve the post title for the first post in the database:
$post_title = $wpdb->get_var( "SELECT post_title FROM $wpdb->posts LIMIT 1" );
Conclusion
In WordPress plugin development, it is often necessary to retrieve specific fields from the database. The WordPress database class, wpdb, provides a simple interface for accessing data in the WordPress database. In this article, we showed you how to use wpdb to retrieve specific fields from the database.
In the previous article, we saw how to use the $wpdb object to connect to the WordPress database and run basic queries. In this article, we will see how to use $wpdb to retrieve specific fields from the database.
When you run a query on the WordPress database, the $wpdb object returns an object with all the fields from the table you queried. This can be a lot of data, and it can be helpful to only retrieve the fields you need.
To do this, you can use the $wpdb->get_results() method. This method takes two parameters: the first is the SQL query, and the second is the output type.
The output type specifies the format in which the data will be returned. The possible values are: OBJECT, ARRAY_A, or ARRAY_N.
OBJECT will return the data as an object, with each field as a property of the object.
ARRAY_A will return the data as an associative array, with each field as a key of the array.
ARRAY_N will return the data as a numeric array, with each field as a value of the array.
The default output type is OBJECT, so if you don’t specify an output type, that’s what you’ll get.
Let’s say we have a table of users, and we want to retrieve the user_id, user_login, and user_email fields for all users. We would use the following query:
$query = “SELECT user_id, user_login, user_email FROM $wpdb->users”;
$results = $wpdb->get_results( $query );
// $results will be an array of objects, each object representing a user
foreach ( $results as $user ) {
echo $user->user_id . ‘: ‘ . $user->user_login . ‘ – ‘ . $user->user_email;
echo ‘
‘;
}
This would output something like:
1: admin – admin@example.com
2: testuser – testuser@example.com
3: anotheruser – anotheruser@example.com
If we wanted to retrieve the same data, but as an associative array, we would use the following query:
$query = “SELECT user_id, user_login, user_email FROM $wpdb->users”;
$results = $wpdb->get_results( $query, ARRAY_A );
// $results will be an array of arrays, each inner array representing a user
foreach ( $results as $user ) {
echo $user[‘user_id’] . ‘: ‘ . $user[‘user_login’] . ‘ – ‘ . $user[‘user_email’];
echo ‘
‘;
}
This would output the same data as before, but with the array keys being the field names:
user_id: admin – admin@example.com
user_login: testuser – testuser@example.com
user_email: anotheruser – anotheruser@example.com
Lastly, let’s say we wanted to retrieve the same data, but as a numeric array. We would use the following query:
$query = “SELECT user_id, user_login, user_email FROM $wpdb->users”;
$results = $wpdb->get_results( $query, ARRAY_N );
// $results will be an array of arrays, each inner array representing a user
foreach ( $results as $user ) {
echo $user[0] . ‘: ‘ . $user[1] . ‘ – ‘ . $user[2];
echo ‘
‘;
}
This would output the same data as before, but with the array values being the field values:
1: admin – admin@example.com
2: testuser – testuser@example.com
3: anotheruser – anotheruser@example.com
As you can see, the $wpdb->get_results() method is a powerful way to retrieve specific fields from the WordPress database.
wpdb in WordPress Plugin
Now that we know how to connect to the WordPress database using wpdb, let’s take a look at how to retrieve specific fields from the database.
To do this, we will use the get_results() method. This method accepts two parameters: the SQL query and the output type.
The SQL query is the query that you want to run on the database. The output type is the way in which you want the results to be outputted. The options for this are: OBJECT, ARRAY_A, ARRAY_N.
OBJECT will output the results as an object. ARRAY_A will output the results as an associative array. ARRAY_N will output the results as a numeric array.
For our example, we will retrieve the post title and post content for all posts in the database. The SQL query for this would be:
SELECT post_title, post_content FROM wp_posts
And the code to retrieve this data would be:
$results = $wpdb->get_results( “SELECT post_title, post_content FROM wp_posts”, OBJECT );
This would output the data as an object. To output the data as an associative array, we would use:
$results = $wpdb->get_results( “SELECT post_title, post_content FROM wp_posts”, ARRAY_A );
And to output the data as a numeric array, we would use:
$results = $wpdb->get_results( “SELECT post_title, post_content FROM wp_posts”, ARRAY_N );
Once we have retrieved the data, we can loop through it and output it however we want.
If we wanted to output the post title and post content for all posts in the database, we would use the following code:
foreach ( $results as $result ) { echo $result->post_title; echo $result->post_content; }
This would output the post title and post content for all posts in the database.
If we wanted to output the post title and post content for all posts in the database as a list, we would use the following code:
- foreach ( $results as $result ) {
- echo $result->post_title; echo $result->post_content;
}
This would output the post title and post content for all posts in the database as a list.
You can also use the get_var() method to retrieve a single value from the database. This method accepts three parameters: the SQL query, the output type and the column number.
The SQL query is the query that you want to run on the database. The output type is the way in which you want the results to be outputted. The options for this are: OBJECT, ARRAY_A, ARRAY_N.
The column number is the number of the column that you want to retrieve the data from. The first column is 0, the second column is 1 and so on.
For our example, we will retrieve the post title for the first post in the database. The SQL query for this would be:
SELECT post_title FROM wp_posts LIMIT 1
And the code to retrieve this data would be:
$result = $wpdb->get_var( “SELECT post_title FROM wp_posts LIMIT 1”, 0, 0 );
This would output the data as a string. To output the data as an integer, we would use:
$result = $wpdb->get_var( “SELECT post_title FROM wp_posts LIMIT 1”, 0, 1 );
And to output the data as a float, we would use:
$result = $wpdb->get_var( “SELECT post_title FROM wp_posts LIMIT 1”, 0, 2 );
Once we have retrieved the data, we can output it however we want.
If we wanted to output the post title for the first post in the database, we would use the following code:
echo $result;
This would output the post title for the first post in the database.
You can also use the get_row() method to retrieve a single row from the database. This method accepts three parameters: the SQL query, the output type and the row number.
The SQL query is the query that you want to run on the database. The output type is the way in which you want the results to be outputted. The options for this are: OBJECT, ARRAY_A, ARRAY_N.
The row number is the number of the row that you want to retrieve the data from. The first row is 0, the second row is 1 and so on.
For our example, we will retrieve the post title and post content for the first post in the database. The SQL query for this would be:
SELECT post_title, post_content FROM wp_posts LIMIT 1
And the code to retrieve this data would be:
$result = $wpdb->get_row( “SELECT post_title, post_content FROM wp_posts LIMIT 1”, OBJECT, 0 );
This would output the data as an object. To output the data as an associative array, we would use:
$result = $wpdb->get_row( “SELECT post_title, post_content FROM wp_posts LIMIT 1”, ARRAY_A, 1 );
And to output the data as a numeric array, we would use:
$result = $wpdb->get_row( “SELECT post_title, post_content FROM wp_posts LIMIT 1”, ARRAY_N, 2 );
Once we have retrieved the data, we can output it however we want.
If we wanted to output the post title and post content for the first post in the database, we would use the following code:
echo $result->post_title; echo $result->post_content;
This would output the post title and post content for the first post in the database.
You can also use the get_col() method to retrieve a single column from the database. This method accepts three parameters: the SQL query, the output type and the column number.
The SQL query is the query that you want to run on the database. The output type is the way in which you want the results to be outputted. The options for this are: OBJECT, ARRAY_A, ARRAY_N.
The column number is the number of the column that you want to retrieve the data from. The first column is 0, the second column is 1 and so on.
For our example, we will retrieve the post title for all posts in the database. The SQL query for this would be:
SELECT post_title FROM wp_posts
And the code to retrieve this data would be:
$results = $wpdb->get_col( “SELECT post_title FROM wp_posts”, 0 );
This would output the data as a string. To output the data as an integer, we would use:
$results = $wpdb->get_col( “SELECT post_title FROM wp_posts”, 1 );
And to output the data as a float, we would use:
$results = $wpdb->get_col( “SELECT post_title FROM wp_posts”, 2 );
Once we have retrieved the data, we can loop through it and output it however we want.
If we wanted to output the post title for all posts in the database, we would use the following code:
foreach ( $results as $result ) { echo $result; }
This would output the post title for all posts in the database.
You can also use the get_results() method to retrieve multiple rows from the database. This method accepts three parameters: the SQL query, the output type and the number of rows.
The SQL query is the query that you want to run on the database. The output type is the way in which you want the results to be outputted. The options for this are: OBJECT, ARRAY_A, ARRAY_N.
The number of rows is the number of rows that you want to retrieve the data from. The first row is 0, the second row is 1 and so on.
For our example, we will retrieve the post title and post content for the first three posts in the database. The SQL query for this would be:
SELECT post_title, post_content FROM wp_posts LIMIT 3
And the code to retrieve this data would be:
$results = $wpdb->get_results( “SELECT post_title, post_content FROM wp_posts LIMIT 3”, OBJECT );
This would output the data as an object. To output the data as an associative array, we would use:
$results = $wpdb->get_results( “SELECT post_title, post_content FROM wp_posts LIMIT 3”, ARRAY_A );
