Wordpress - Order by author if different than "admin" - php

Question

In "category.php" file I need to order my posts in this strange way:
First all the posts where author is different than "admin" (in alphabetical order by title)
Than all the post by "admin" (in the same alphabetical order)
Here is the standard code I use to do my query:
<?php global
$wp_query;
query_posts(
array_merge(
array('orderby' => 'title', 'order' => 'ASC'),
$wp_query->query
)
);
?>
Any idea about how to accomplish it without nesting two queries?
Thanks in advance!
EDIT: Following is some code that was tried, as suggested by Sepster in a previous version of his answer. But at the moment this code starts showing all the posts from 'admin' (instead of the others) until the posts with author different than 'admin' come. At that point it breaks the results and jump to the next page of results.
<?php
global $wp_query;
query_posts(
array_merge(
array('orderby' => 'title', 'order' => 'ASC'),
$wp_query->query
)
);
$adminPosts = false;
for ($i=1; $i<=2; $i++) {
while ( $wp_query->have_posts() ) {
$wp_query->the_post();
$author = get_the_author();
if ($author == 'admin' && $adminPosts == false) break;
if ($author != 'admin' && $adminPosts == true) break;
// ALL MY STUFF
} // end while
rewind_posts();
$adminPosts=true;
} // end FOR
?>

Answer 1

Update:
I've finally come up with a somewhat workable solution for this, but it's fair to say this really is an excercise in academics; Yes, it's do-able without executing a second loop, but really, it's pretty convoluted.
The solution is, in summary
Develop a custom SQL statement that will return the rows in the order required.
This is because in SQL, the only way to get the results in the order you need is by doing a UNION of your two subsets. To my knowledge there's no way of doing that using the "normal" WP query operations.
Execute this query, and loop over its results rather than a standard "the loop".
This is because we're getting back a recordset, rather than a WP_Query object.
Set the "Blog pages show at most X posts" setting to 1.
(on /wp-admin/options-reading.php)
A common complaint is pagination breaking when using custom queries (incidentally, the query_posts() method you're using is susceptible to this issue).
There are numerous turorials on how to do this properly, eg:
https://codex.wordpress.org/Making_Custom_Queries_using_Offset_and_Pagination
https://codex.wordpress.org/Pagination#Troubleshooting_Broken_Pagination
The first of those recommends the implementation of "Offset and Manual Pagination".
The closest I've found to an implementation of this in conjunction with a custom SQL statement is this https://wordpress.stackexchange.com/a/28717. I've borrowed heavily from this answer (and so I recommend you go over and give it an up-vote!).
However, this technique (among other more "standard" custom query approaches) suffers from a known behaviour where WP produces a 404 on the final page (if I understand correctly, because WP is still using its own query and associated max-page=posts-per-page/posts calculations to map between the page number in the URL and the delivered content).
Refer http://wordpress.org/support/topic/explanation-and-workaround-for-error-404-on-category-pagination?replies=14 for details about this issue, and a proposed solution (which unfortunately won't work for our custom SQL approach).
A known "work-around" for this issue is to reduce the number of posts-per-page to 1, as per eg http://wordpress.org/support/topic/custom-post-type-pagination-404-on-last-page
So, assuming you're happy with a global setting of 1 posts-per-page (remember you'd need to override this manually in your custom queries), here's the code:
functions.php:
...
function get_users_posts_last($userDisplayName = 'Admin', $categoryName = '') {
global $wpdb, $paged, $max_num_pages;
$paged = (get_query_var('paged')) ? get_query_var('paged') : 1;
$post_per_page = 5;
$offset = ($paged - 1)*$post_per_page;
$sql = "
SELECT SQL_CALC_FOUND_ROWS q.* FROM
(
(
SELECT
p.*
FROM
{$wpdb->posts} p
INNER JOIN {$wpdb->users} u ON p.post_author = u.ID
LEFT JOIN {$wpdb->term_relationships} tr ON p.ID = tr.object_id
LEFT JOIN {$wpdb->term_taxonomy} tt ON tr.term_taxonomy_id = tt.term_taxonomy_id
LEFT JOIN {$wpdb->terms} t ON tt.term_id = t.term_id
WHERE
tt.taxonomy = 'category'
AND p.post_status = 'publish'
AND p.post_type = 'post'
AND u.display_name != '{$userDisplayName}'
" . ( $categoryName != '' ? "AND t.name = '{$categoryName}'" : "" ) . "
ORDER BY
p.post_title ASC
)
UNION
(
SELECT
p.*
FROM
{$wpdb->posts} p
INNER JOIN {$wpdb->users} u ON p.post_author = u.ID
LEFT JOIN {$wpdb->term_relationships} tr ON p.ID = tr.object_id
LEFT JOIN {$wpdb->term_taxonomy} tt ON tr.term_taxonomy_id = tt.term_taxonomy_id
LEFT JOIN {$wpdb->terms} t ON tt.term_id = t.term_id
WHERE
tt.taxonomy = 'category'
AND p.post_status = 'publish'
AND p.post_type = 'post'
AND u.display_name = '{$userDisplayName}'
" . ( $categoryName != '' ? "AND t.name = '{$categoryName}'" : "" ) . "
ORDER BY
p.post_title ASC
)
) q
LIMIT {$offset}, {$post_per_page};
";
$sql_result = $wpdb->get_results( $sql, OBJECT);
$sql_posts_total = $wpdb->get_var( "SELECT FOUND_ROWS();" );
$max_num_pages = ceil($sql_posts_total / $post_per_page);
return $sql_result;
}
...
category.php:
...
$postList = get_users_posts_last('admin'); // Note you can also pass a category name if necessary
if($postList) {
global $post;
foreach( $postList as $key=>$post ) {
setup_postdata($post);
// Render the post here
?>
<header class='entry-header'><h1 class='entry-title'><?php the_title(); ?></h1></header>
<div class='entry-content'><?php the_content(); ?></div>
<?php
}
// Render pagination here
?>
<div class="navigation">
<div class="previous panel"><?php previous_posts_link('« Previous page',$max_num_pages) ?></div>
<div class="next panel"><?php next_posts_link('Next page »',$max_num_pages) ?></div>
</div>
<?php
}
...
Or, just set up two separate queries ;-)