62

I noticed that there are bunch of operator can be use for compare in meta_query. However, I am not quite sure what operator I should use, it is somehow confusing like = and LIKE operator.

I would like to know what exactly each operator mean, and in what condition I should use them.

=
!=
>
>=
<
<=
LIKE
NOT LIKE
IN
NOT IN
BETWEEN
NOT BETWEEN
NOT EXISTS

Thanks.

2 Answers 2

101

The first several work as you would expect:

=   equals
!=  does not equal
>   greater than
>=  greater than or equal to
<   less than
<=  less than or equal to



LIKE and NOT LIKE

LIKE and NOT LIKE are SQL operators that let you add in wild-card symbols, so you could have a meta query that looks like this:

array( 
    'key' => 'name', 
    'value' => 'Pat', 
    'compare' => 'LIKE'
)

This would return all posts where the meta value "name" has the string "Pat". In this case, "Pat" "Patricia" and "Patrick" would all be returned back to you. There's a non-WordPress tutorial explanation here.

Adding the wildcard character % isn't necessary, because it gets added by default like @Herb said in his below answer. Like this: $meta_value = '%' . like_escape( $meta_value ) . '%'; - see source.



IN and NOT IN

IN and NOT IN select any matches that are in (or not in) the given array. So you could do something like this:

array(
    'key'     => 'color', 
    'value'   => array('red', 'green', 'blue') 
    'compare' => 'IN'
)

and it would get all posts that have the color set to either red, green, or blue. Using 'NOT IN' gets the reverse, any posts that have a value set to anything else than what's in the array.

The generated SQL for this would look something like this:

SELECT * FROM posts_meta WHERE value IN ("red", "green", "blue") 



BETWEEN and NOT BETWEEN

BETWEEN and NOT BETWEEN allow you to define a range of values that could be correct, and require you to give two values in an array in your meta_query:

array( 
    'key' => 'price', 
    'value' => array(20,30) 
    'compare' => 'BETWEEN'
)

This will get you all posts where the price is between 20 and 30. This person digs into an example with dates.



NOT EXISTS

NOT EXISTS is just like what it sounds - the meta value isn't set or is set to a null value. All you need for that query is the key and comparison operator:

array( 
    'key' => 'price', 
    'compare' => 'NOT EXISTS'
)

This person needed to query non-existent meta values, and needed them to play nice with others.

Hope this helps!

5
  • 2
    Note: If you're using meta_query array, your keys should not be prefixed with meta_. If you're using $query->meta_key, $query->meta_value, etc. then these should still retain the prefix.
    – Sean
    Aug 20, 2014 at 14:25
  • I can't seem to find an explanation on what the "IN" compare option does. Any idea how that works?
    – Joe
    Mar 9, 2015 at 14:50
  • 2
    @Joe, I don't know why I didn't add anything about "IN" and "NOT IN". I've edited and updated the answer with those comparisons.
    – Jen
    Mar 9, 2015 at 16:05
  • This is a great answer but there are some more options available now-: codex.wordpress.org/Class_Reference/WP_Meta_Query
    – noelmcg
    Aug 28, 2020 at 10:38
  • 'EXISTS' , 'REGEXP', 'NOT REGEXP' and 'RLIKE'
    – noelmcg
    Aug 28, 2020 at 10:39
13

Note that when using a meta_compare value of 'LIKE', WordPress automatically wraps the wildcard character ( % ) around the meta_value string. So the 'Pat%' example could fail to return any results.

2
  • is there info about that in the docs somewhere Herb? Should the example change to remove the %?
    – Jen
    Nov 22, 2013 at 15:47
  • It should, I actually did that right now, see the source, then it gets very clear that Herb is right. @guiniveretoo Apr 8, 2014 at 15:10

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