How to replace OR operator with UNION operator?

Question

Here is my query:

SELECT 
    h.id,
    h.subject,
    h.body matnF,
    h.amount,
    h.keywords tags,
    h.closed,
    h.author_id author,
    h.AcceptedAnswe         


        

Answer 1

You may give it a try:

SELECT h.id, h.subject, h.body matnF, h.amount, h.keywords tags, h.closed, h.author_id author, h.AcceptedAnswer, h.type, h.visibility, h.date_time, v.value AS vote_value, u.reputation, u.user_fname, u.user_lname, u.avatar, (h.author_id = :user_id1) as hasUserId,
(select COALESCE(sum(vv.value),0) from votes vv where h.id = vv.post_id and vv.table_code = '$this->table_code') as total_votes,
(select count(1) from favorites ff where h.type = 0 and h.id = ff.post_id and ff.table_code = '$this->table_code') as total_favorites,
CASE WHEN h.type = 1 THEN '0'
WHEN h.amount IS NULL OR h.author_id = :user_id2 THEN '1'
ELSE EXISTS (select 1 from money m where m.user_id = :user_id3 and m.post_id = h.id) END paid,
CASE WHEN h.type = 0 AND f.id IS NOT NULL THEN '2' ELSE '3' END AS favorite
FROM qanda h
LEFT JOIN votes v ON h.id = v.post_id AND v.user_id = :user_id4 AND v.table_code = '$this->table_code'
LEFT JOIN favorites f ON h.type = 0 AND h.id = f.post_id AND f.user_id = :user_id5 AND f.table_code = '$this->table_code'
LEFT JOIN users u ON h.author_id = u.id and h.visibility = 1
WHERE h.id = :id1 
ORDER BY h.type, /*(tans.id IS NOT NULL) DESC,*/ h.AcceptedAnswer DESC, h.date_time
LIMIT 20

UNION 

SELECT 
*
FROM 
(SELECT h.id, h.subject, h.body matnF, h.amount, h.keywords tags, h.closed, h.author_id author, h.AcceptedAnswer, h.type, h.visibility, h.date_time, v.value AS vote_value, u.reputation, u.user_fname, u.user_lname, u.avatar, (h.author_id = :user_id1) as hasUserId,
(select COALESCE(sum(vv.value),0) from votes vv where h.id = vv.post_id and vv.table_code = '$this->table_code') as total_votes,
(select count(1) from favorites ff where h.type = 0 and h.id = ff.post_id and ff.table_code = '$this->table_code') as total_favorites,
CASE WHEN h.type = 1 THEN '0'
WHEN h.amount IS NULL OR h.author_id = :user_id2 THEN '1'
ELSE EXISTS (select 1 from money m where m.user_id = :user_id3 and m.post_id = h.id) END paid,
CASE WHEN h.type = 0 AND f.id IS NOT NULL THEN '2' ELSE '3' END AS favorite
FROM qanda h
LEFT JOIN votes v ON h.id = v.post_id AND v.user_id = :user_id4 AND v.table_code = '$this->table_code'
LEFT JOIN favorites f ON h.type = 0 AND h.id = f.post_id AND f.user_id = :user_id5 AND f.table_code = '$this->table_code'
LEFT JOIN users u ON h.author_id = u.id and h.visibility = 1
WHERE h.id = :id2 
ORDER BY h.type, /*(tans.id IS NOT NULL) DESC,*/ h.AcceptedAnswer DESC, h.date_time
LIMIT 20) t;

Note: Replace UNION by UNION ALL if you want to allow duplicates in your final result set.