AND and OR query in WordPress wpdb

WP_Query does both ANDs and ORs, but often you have no choice, it does whatever makes the most sense for normal queries. OR is rather rare, the default is typically AND.

However, it appears your dropdowns are either categories or some sort of taxonomy. The ‘tax_query’ arguments for WP_Query support user selectable logic, so there is no problem doing what you are doing.

FWIW, in case you do come across something WP_Query cannot handle, there are several filters for various SQL clauses that make up the query. You can hook these filters and alter what WP_Query came up with, so you should be able to compose almost any SQL query imaginable.

Hi bcworkz, thanks for getting back to me. Here is a snippet of what I have.

<?php //the_content();

	if ($_GET["productType"] || $_GET["productGroup"] || $_GET["productCountry"]) {
		$productType 		= $_GET["productType"];
		$productGroup 	= $_GET["productGroup"];
		$productCountry 	= $_GET["productCountry"];
	} else {
		$productType 		= ' ';
		$productGroup 	= ' ';
	}

$args = array(
		'post_type' => 'product',
		'posts_per_page' => -1,
		'orderby' => 'title',
		'order' => 'ASC',
		'relation'=>'AND',
		'meta_query' => array(
		       array(
		           'key' 		=>	'product_type',
		           'value' 		=> 	$productType,
		           'compare' 	=> 	'LIKE'
		       ),
		       array(
				    'key'		=>	'crop_group',
				    'value'		=>	$productGroup,
				    'compare' 	=> 	'LIKE'
				),
		       array(
				    'key'		=>	'country',
				    'value'		=>	$productCountry,
				    'compare' 	=> 	'LIKE'
				)
		    )
		);
?>

<form name="x" action="" method="GET" class="search-results-form" >
  <div>
  	<select name="solutionCountry" class="search-product-type">
		<option value="South Africa">South Africa</option>
		<option value="Angola">Angola</option>
		<option value="Botswana">Botswana</option>
		<option value="Malawi">Malawi</option>
		<option value="Mozambique">Mozambique</option>
		<option value="Namibia">Namibia</option>
		<option value="Zambia">Zambia</option>
		<option value="Zimbabwe">Zimbabwe</option>
  	</select>
  </div>
  or
  <div>
  	<select name="solutionType" class="search-product-type">
		<option value="Product1">Product 1</option>
		<option value="Product2">Product 2</option>
		<option value="Product3">Product 3</option>
		<option value="Product4">Product 4</option>
		<option value="Product5">Product 5</option>
  	</select>
  </div>
  or
  <div>
	  <select name="solutionGroup" class="search-product-group">
			<option value="Group1">Group1</option>
			<option value="Group2">Group2</option>
			<option value="Group3">Group3</option>
			<option value="Group4">Group4</option>
			<option value="Group5">Group5</option>
	  </select>
  </div> 

  <input type="submit" value="SEARCH" class="submit-button btn" />
</form>

<?php
	// return the results
	$loop = new WP_Query( $args ); ?>
	<ul>
		<?php while ( $loop->have_posts() ) : $loop->the_post(); ?>
			<li>
				<strong><a href="<?php echo get_permalink(); ?>"><?php the_title(); ?></a> - <?php the_field('solution_type'); ?></strong><br>
				<?php the_field('solution_description'); ?><br><br>
			</li>
		<?php endwhile; ?>
		<?php wp_reset_query(); ?>
	</ul>
<?php } ?>

If it is possible to use WP_Query with AND and OR, I’d appreciate some help.

Looks good for the most part! The only thing I see is the ‘relation’ argument needs to be inside the ‘meta_query’ array:

//...
'orderby' => 'title',
'order' => 'ASC',
'meta_query' => array(
	'relation' => 'AND',
	array(
		'key' 		=>	'product_type',
		'value' 	=> 	$productType,
		'compare' 	=> 	'LIKE'
	),
//...

of course the relation can be ‘OR’ if you like.

Thanks bcworkz. I will give that a shot.
Perhaps it is the logic that I cannot seem to wrap my head around and the fact that I have not used WP_Query much like this, but will this ensure that if I select one dropdown and search or both dropdowns, it will do the query across both selected options?

Do I not need both AND and OR to do the comparison?

As it stands with AND, all 3 selections must match a post for it to be returned. If the OR relation is specified, any one or more of the selections must match a post for it to be returned. You cannot provide both AND and OR relations in the same query. More complex logic is not possible with meta_query arguments, but is possible by filtering ‘posts_where_paged’.

If not all selections are required, you’ll need to restructure your program flow a bit. You must never try to assign non-existent values. For starters, you are assigning all 3 values if any one of them exist. If one of the others do not exist, the assignment statement will throw an error. The safest way to allow any possible combination of selection or non-selection is something like this for each possible value: if(array_key_exists("productType", $_GET)) $productType = $_GET["productType"];.

You will then also need to selectively build the meta_query array depending on which selections were provided. Initialize the array with $meta_args = array('relation' => 'AND'); (or OR if that is what you want), then add in each argument array if the argument was selected. This statement could go into the same array key exists conditional:

$meta_args[] = array(
   'key' => 'product_type',
   'value' => $productType,
   'compare' => 'LIKE',
);

Then of course the full query $args array would include 'meta_query' => $meta_args,

One minor improvement since the array assignment is in the same conditional as the $productType assignment is to not even bother with $productType and define the array directly with $_GET["productType"], that is unless you need $productType for other reasons.

Thanks bcworkz, for the lengthy explanation, much appreciated! I will give your instructions a bash now and see how it goes.