Query posts by Author and/or by Tag

Question

Your first query is very strange. You seem to be mixing meta_query parameters with other WP_Query arguments. You can’t do that. author is not a valid component of a meta_query, neither is tag. The correct meta_query, if I am interpreting this right, wouldn’t even be a meta query. You are dealing with a taxonomy, a tag, so you need a tax_query.

'tax_query' => array(
  array(
    'taxonomy' => 'post_tag',
    'field' => 'slug',
    'terms' => $nametag
  )
)

Unfortunately, if you build a complete query with an author, you get an AND between the tax query and the author, and you need an OR.

$query = new WP_Query( 
  array( 
    'author' => 1, 
    'tax_query' => array(
      array(
        'taxonomy' => 'post_tag',
        'field' => 'slug',
        'terms' => 'depo'
      )
    )
  )
);

That will give you the following query.

SELECT SQL_CALC_FOUND_ROWS wp_posts.ID 
FROM wp_posts 
INNER JOIN wp_term_relationships ON (wp_posts.ID = wp_term_relationships.object_id) 
WHERE 1=1 
AND ( wp_term_relationships.term_taxonomy_id IN (57) ) 
AND (wp_posts.post_author = 1) 
AND wp_posts.post_type="post" 
AND (wp_posts.post_status="publish") 
GROUP BY wp_posts.ID 
ORDER BY wp_posts.post_date DESC LIMIT 0, 5

That is not your data, but it is illustrative.

The AND right here– AND (wp_posts.post_author = 1)— is a problem. You need that to be an OR. In fact you need it in parenthesis too …

SELECT SQL_CALC_FOUND_ROWS wp_posts.ID 
FROM wp_posts 
INNER JOIN wp_term_relationships ON (wp_posts.ID = wp_term_relationships.object_id) 
WHERE 1=1 
AND ( 
  (wp_term_relationships.term_taxonomy_id IN (57)) 
  OR (wp_posts.post_author = 1) 
)
AND wp_posts.post_type="post" 
AND (wp_posts.post_status="publish") 
GROUP BY wp_posts.ID 
ORDER BY wp_posts.post_date DESC LIMIT 0, 5

You would have to create a filter for posts_where to correct that, but since you are already writing your own SQL I will leave that alone. I think you can make things work using the query above as a reference.