Custom Database Queries in WordPress

Custom Database Queries in WordPress

An overview of the $wpdb object

Custom Database Queries in WordPressTopher DeRosia

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Developer and Documenter from


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Should I write my own custom queries with WordPress?


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NO!WP_Query is efficient and secure.


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Should I use custom database tables with WordPress?


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NO!WordPress has an excellent database structure that should accommodate nearly any data.


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


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Why would you write a custom query?

1. You want something really crazy from WordPress tables.

2. You’re accessing data from custom tables.


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Why would you use custom tables?

1. You need to utilize an existing data set.

2. Whatever you’re building is so weird that it can’t use WordPress’ table structure.


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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 );


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What do we do with a table?

● Select● Insert● Update● Delete

Also some debugging and stats analysis.


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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.


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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.


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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


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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


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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.


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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


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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.


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Prepared Statements

Prepared statements allow for much greater security.

$wpdb->query( $wpdb->prepare(

"DELETE FROM $wpdb->postmetaWHERE post_id = %dAND meta_key = %s",

13, 'gargle’ )

);

NOTE: $wpdb knows the names of WordPress tables


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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

) );


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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 ); ?>


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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


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https://codex.wordpress.org/Class_Reference/wpdb

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Custom Database Queries in WordPress