Custom Database Queries in WordPress

Custom Database Queries
in WordPress
An overview of the $wpdb object
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

Developer and Documenter from
Topher DeRosia
@topher1kenobe

Should I write my own custom
queries with WordPress?
Topher DeRosia
@topher1kenobe

NO!
WP_Query is efficient and secure.
Topher DeRosia
@topher1kenobe

Should I use custom database
tables with WordPress?
Topher DeRosia
@topher1kenobe

NO!
WordPress has an excellent database structure
that should accommodate nearly any data.
Topher DeRosia
@topher1kenobe

Learn the rules like a pro, so you can break them like an artist” -- Pablo
Picasso
Topher DeRosia
@topher1kenobe

Why would you write a custom query?
1. You want something really crazy from
WordPress tables.
1. You’re accessing data from custom tables.
Topher DeRosia
@topher1kenobe

Why would you use custom tables?
1. You need to utilize an existing data set.
1. Whatever you’re building is so weird that it
can’t use WordPress’ table structure.
Topher DeRosia
@topher1kenobe

How do we talk to MySQL inside
WordPress?
The $wpdb object is instantiated very early and
provides a number of methods for communicating
with the database.
Example:
$results = $wpdb->get_results( 'SELECT * FROM
wp_options WHERE option_id = 1', OBJECT );
Topher DeRosia
@topher1kenobe

What do we do with a table?
● Select
● Insert
● Update
● Delete
Also some debugging and stats analysis.
Topher DeRosia
@topher1kenobe

SELECT
get_var()
$wpdb->get_var( $query, column_offset, row_offset );
The get_var function returns a single variable from the database. The
entire result of the query is cached for later use. Returns NULL if no
result is found.
get_row()
$wpdb->get_row($query, output_type, row_offset);
Retrieves an entire row. Can return an object, associative array, or
numerically indexed array. Caches all matching rows.
Topher DeRosia
@topher1kenobe

SELECT
get_col()
$wpdb->get_col( $query, column_offset );
Returns a one dimensional array of a column.
get_results()
$wpdb->get_results( $query, output_type );
Generic, multiple row results can be pulled from the database with
get_results. Returns the entire query result as an array.
Topher DeRosia
@topher1kenobe

INSERT
$wpdb->insert( $table, $data, $format );
$wpdb->insert(
'table',
array(
'column1' => 'value1',
'column2' => 123
),
array(
'%s',
'%d'
)
);
This function returns false if the row could not be inserted. Otherwise, it returns the number of
affected rows (which will always be 1).
After insert, the ID generated for the AUTO_INCREMENT column can be accessed with:
$wpdb->insert_id
Topher DeRosia
@topher1kenobe

UPDATE
$wpdb->update( $table, $data, $where, $format = null, $where_format = null );
$wpdb->update(
'table',
array(
'column1' => 'value1', // string
'column2' => 'value2' // integer (number)
),
array( 'ID' => 1 ),
array(
'%s', // value1
'%d' // value2
),
array( '%d' )
);
Return values: This function returns the number of rows updated, or false if there is an error. Keep in mind that if the $data
matches what is already in the database, no rows will be updated, so 0 will be returned. Because of this, you should
probably check the return with false === $result
Topher DeRosia
@topher1kenobe

DELETE
$wpdb->delete( $table, $where, $where_format = null );
$wpdb->delete( 'table', array( 'ID' => 1 ), array( '%d' ) );
Returns the number of rows updated, or false on error.
Topher DeRosia
@topher1kenobe

REPLACE
$wpdb->replace( $table, $data, $format );
$wpdb->replace(
'table',
array(
'indexed_id' => 1,
'column1' => 'value1',
'column2' => 123
),
array(
'%d',
'%s',
'%d'
)
);
After replace, the ID generated for the AUTO_INCREMENT column can be accessed with:
$wpdb->insert_id
Topher DeRosia
@topher1kenobe

query()
$wpdb->query( $query );
The query() function allows you to send any query.
IMPORTANT: Returns an integer value indicating the number of rows
affected/selected for SELECT, INSERT, DELETE, UPDATE, etc.
For CREATE, ALTER, TRUNCATE and DROP SQL statements, (which
affect whole tables instead of specific rows) this function returns TRUE
on success.
If a MySQL error is encountered, the function will return FALSE.
Topher DeRosia
@topher1kenobe

Prepared Statements
Prepared statements allow for much greater security.
$wpdb->query(
$wpdb->prepare(
"
DELETE FROM $wpdb->postmeta
WHERE post_id = %d
AND meta_key = %s
",
13, 'gargle’
)
);
NOTE: $wpdb knows the names of WordPress tables
Topher DeRosia
@topher1kenobe

Prepared Statements
Another example:
$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
) );
Topher DeRosia
@topher1kenobe

Show and Hide MySQL errors
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 ); ?>
Topher DeRosia
@topher1kenobe

Important details
● get_results() is the most flexible method, BUT
● Use prepare() whenever possible
● Be consistent
● Read everything on the Codex
https://codex.wordpress.org/Class_Reference/wpdb
Topher DeRosia
@topher1kenobe

THANKS FOR
LISTENING
Topher DeRosia
@topher1kenobe
http://topher1kenobe.com
Follow me @topher1kenobe

Custom Database Queries in WordPress

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