The document discusses using custom database queries in WordPress. It introduces the $wpdb object, which allows communicating with the database. It advises that WP_Query is usually better than custom queries. The $wpdb methods for querying (select, insert, update, delete) and preparing statements are covered. Best practices like using prepare() for security are emphasized.

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

2. Developer and Documenter from
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

3. Should I write my own custom
queries with WordPress?
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

4. NO!
WP_Query is efficient and secure.
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

5. Should I use custom database
tables with WordPress?
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

6. NO!
WordPress has an excellent database structure
that should accommodate nearly any data.
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

7. Learn the rules like a pro, so you can break them like an artist” -- Pablo
Picasso
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

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

9. 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.
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

10. 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 );
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

11. What do we do with a table?
● Select
● Insert
● Update
● Delete
Also some debugging and stats analysis.
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

12. 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.
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

13. 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.
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

14. 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
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

15. 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
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

16. 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.
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

17. 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
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

18. 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.
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

19. 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
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

20. 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
) );
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

21. 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 ); ?>
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

22. 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
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe

23. THANKS FOR
LISTENING
Custom Database Queries in WordPress
Topher DeRosia
@topher1kenobe
http://topher1kenobe.com
Follow me @topher1kenobe