Searching custom fields in WordPress with meta_query

There have been quite a few incredibly useful features that were introduced in WordPress version 3.0, which came out over a year ago. However, perhaps my favorite didn’t come till half a year later when version 3.1 was released.
Previously, searching posts, pages or custom post types using custom field required a more-than-reasonable amount of work by directly querying the database with lots of nested SQL, which was fairly cumbersome. Fortunately, a new parameter was introduced into the query string arsenal streamlining this process.
If you look in the WordPress Codex for WP_Query, you’ll see a new(ish) parameter called ‘meta_query’, which does exactly that–queries meta data for a post. It can search singular fields, as well as multiple fields, and handles all your typical SQL operators, e.g., =, !=, LIKE, BETWEEN, and IN. As a bonus, meta_query also plays nicely with the search parameter, ‘s’, and works with custom post types and custom taxonomies.
There are two ways it can be used.

For singular queries:

$query = new WP_Query( array ( 'meta_key' => 'meta_value' ) );

For multiple queries:

$query = new WP_Query( array(
	'post_type' =>; 'food',
	'meta_query' => array(
		array(
			'key' => 'color',
			'value' => 'brown',
			'compare' => 'NOT LIKE'
		),
		array(
			'key' => 'taste',
			'value' => 'sweet'
			'compare' => '='
		),
	)
);

Note that in that first example, the ‘compare’ key is left out in the second array. If nothing is set for ‘compare’, the default value of ‘=’ will be used.