WP How can I combine multipe query? - wordpress

Question

I like to combine multiple query into one result.
$args_a and $args_b in below code are simplified to summarize my question. I like to combine 2 or more query in one result.
They should not be overwritten each other, so I think "merge" is not proper method to combine this case.
Now, how can I combine them together?
<?php
$args_a = array(
'posts_per_page' => 9,
'paged' => $paged,
'category_name' => 'shinmatsudo',
'category__in' => array( 227 ),
'category__not_in' => array( 3 ),
'meta_query' => array(
'relation' => 'AND',
array(
'key' => '1b',
'compare' => 'NOT EXISTS'
),
array(
'key' => '1d',
'compare' => 'NOT EXISTS'
),
),
);?>
<?php
$args_b = array(
'paged' => $paged,
'posts_per_page' => 9,
'category_name' => 'matsudo',
'category__in' => array( 329 ),
'category__not_in' => array( 3 ),
'meta_query' => array(
'relation' => 'and',
array(
'key'=> '2a',
'value' => array('2020-02-01' , '2020-06-01'),
'compare' => 'BETWEEN',
'type' => 'DATE',
),
),
);
?>
<?php
global $post;
$my_posts= get_posts($args_b);
$my_posts= get_posts($args_a);
foreach($my_posts as $post):setup_postdata($post);?>
<div id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
<h1 class="entry-title"><?php the_title(); ?></h1>
</div>
<?php endforeach; ?>
<?php wp_reset_postdata(); ?>

Answer 1

The problem your code has is you are overwriting $my_posts variable. Think about what your code is doing:
global $post;
$my_posts= get_posts($args_b);
$my_posts= get_posts($args_a);
You are reassigning $my_posts to the second get_posts so the $args_b will always be overwritten.
You can try using array_merge() to take the results of both get_posts and combine them into a single array.
global $post;
$my_posts= array_merge( get_posts($args_b), get_posts($args_a) );
foreach($my_posts as $post):setup_postdata($post);?>
<div id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
<h1 class="entry-title"><?php the_title(); ?></h1>
</div>
<?php endforeach; ?>
<?php wp_reset_postdata(); ?>