Using Union and Order by Clause in MySQL

Using union and order by clause in mysql

You can do this by adding a pseudo-column named rank to each select, that you can sort by first, before sorting by your other criteria, e.g.:

select *
from (
    select 1 as Rank, id, add_date from Table 
    union all
    select 2 as Rank, id, add_date from Table where distance < 5
    union all
    select 3 as Rank, id, add_date from Table where distance between 5 and 15
) a
order by rank, id, add_date desc

Apply ORDER BY on a UNION (Mysql)

SELECT *
FROM (
(SELECT * FROM user_relation WHERE from_user_id = 1)
UNION
(SELECT * FROM user_relation WHERE to_user_id = 1)
) AS i
ORDER BY trust_degree

You have to assign an alias to your select. But in this case a UNION is not necessary and could be replaced by a simple OR, as @Karoly Horvath points out in his comment. The resulting query would look like this:

SELECT 
 * 
FROM user_relation 
WHERE from_user_id = 1 OR to_user_id = 1 
ORDER BY trust_degree

Error with ORDER BY clause using UNION in MySQL

The results of your UNION do not include any fields from table 'u', so those results cannot be sorted by table 'u' fields.

You could perhaps perform the UNION and then re-join the results to table 'u', and then use that to sort the results by table 'u' fields. A similar issue exists for sorting on
course.fullname, so that would need to be joined back in, too.

SELECT x.id, x.userid, x.status, x.timestart, x.timeend, x.courseid, x.enrolid, x.roleid
FROM ((SELECT ue.id, ue.userid, ue.status, ue.timestart, ue.timeend, e.courseid,
        e.id AS enrolid, ra.roleid
       FROM user_enrolments ue
         JOIN enrol e ON e.id = ue.enrolid
         JOIN course c ON c.id = e.courseid
         JOIN user u ON u.id = ue.userid
         JOIN context ct ON ct.instanceid = c.id
         LEFT JOIN role_assignments ra ON ra.userid = u.id 
           AND ra.contextid = ct.id 
           AND ra.itemid = e.id
       WHERE e.customint1 = 1 AND u.deleted = 0 
           AND ct.contextlevel = 50 AND (ue.status = 0 OR ue.status = 1)) 
       UNION
       (SELECT de.enrolid AS id, de.userid, de.status, de.date_ini, de.date_fin, 
        de.courseid, de.enrolid, de.roleid
        FROM deleted_enrols de
          JOIN user u ON u.id = de.userid
         WHERE userid = ANY (SELECT userid FROM local_users WHERE clientid = 1))
) x
  JOIN user z ON z.id = x.userid
  JOIN course d ON d.id = x.courseid
ORDER BY z.firstname, z.lastname, d.fullname LIMIT 0, 100

How to use ORDER BY inside UNION

Something like this should work in MySQL:

SELECT a.*
  FROM ( 
         SELECT ...  FROM ... ORDER BY ... 
       ) a
 UNION ALL 
SELECT b.*
  FROM ( 
         SELECT ...  FROM ... ORDER BY ... 
       ) b

to return rows in an order we'd like them returned. i.e. MySQL seems to honor the ORDER BY clauses inside the inline views.

But, without an ORDER BY clause on the outermost query, the order that the rows are returned is not guaranteed.

If we need the rows returned in a particular sequence, we can include an ORDER BY on the outermost query. In a lot of use cases, we can just use an ORDER BY on the outermost query to satisfy the results.

But when we have a use case where we need all the rows from the first query returned before all the rows from the second query, one option is to include an extra discriminator column in each of the queries. For example, add ,'a' AS src in the first query, ,'b' AS src to the second query.

Then the outermost query could include ORDER BY src, name, to guarantee the sequence of the results.

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FOLLOWUP

In your original query, the ORDER BY in your queries is discarded by the optimizer; since there is no ORDER BY applied to the outer query, MySQL is free to return the rows in whatever order it wants.

The "trick" in query in my answer (above) is dependent on behavior that may be specific to some versions of MySQL.

Test case:

populate tables

CREATE TABLE foo2 (id INT PRIMARY KEY, role VARCHAR(20)) ENGINE=InnoDB;
CREATE TABLE foo3 (id INT PRIMARY KEY, role VARCHAR(20)) ENGINE=InnoDB;

INSERT INTO foo2 (id, role) VALUES 
  (1,'sam'),(2,'frodo'),(3,'aragorn'),(4,'pippin'),(5,'gandalf');
INSERT INTO foo3 (id, role) VALUES 
  (1,'gimli'),(2,'boromir'),(3,'elron'),(4,'merry'),(5,'legolas');

query

SELECT a.*
  FROM ( SELECT s.id, s.role
           FROM foo2 s
          ORDER BY s.role
       ) a
 UNION ALL
SELECT b.*
  FROM ( SELECT t.id, t.role
           FROM foo3 t
          ORDER BY t.role
       ) b

resultset returned

    id  role     
 ------  ---------
      3  aragorn  
      2  frodo    
      5  gandalf  
      4  pippin   
      1  sam      
      2  boromir  
      3  elron    
      1  gimli    
      5  legolas  
      4  merry    

The rows from foo2 are returned "in order", followed by the rows from foo3, again, "in order".

Note (again) that this behavior is NOT guaranteed. (The behavior we observer is a side effect of how MySQL processes inline views (derived tables). This behavior may be different in versions after 5.5.)

If you need the rows returned in a particular order, then specify an ORDER BY clause for the outermost query. And that ordering will apply to the entire resultset.

As I mentioned earlier, if I needed the rows from the first query first, followed by the second query, I would include a "discriminator" column in each query, and then include the "discriminator" column in the ORDER BY clause. I would also do away with the inline views, and do something like this:

SELECT s.id, s.role, 's' AS src
  FROM foo2 s
 UNION ALL
SELECT t.id, t.role, 't' AS src
  FROM foo3 t
 ORDER BY src, role

Mysql multiple ORDER BY with UNION

Try this

SELECT n.nid, max(na.gid) as mid,fav.field_date_posted_value, UNIX_TIMESTAMP(fav.field_date_posted_value) as pdate, 1 as ob FROM `node` as n
JOIN nodeaccess AS na ON na.nid = n.nid
LEFT JOIN field_data_field_date_posted AS fav ON fav.entity_id = n.nid
WHERE (na.gid IN(10,11) AND (n.status = '1') AND (n.type IN  ('article','blog', 'events', 'media', 'press_releases', 'expert_speak', 'feature', 'case_study', 'news', 'the_igtb_series', 'trend', 'white_paper')) )
GROUP BY n.nid 


UNION ALL

SELECT n.nid, max(na.gid) as mid,fav.field_date_posted_value, UNIX_TIMESTAMP(fav.field_date_posted_value) as pdate, 2 as ob FROM `node` as n
JOIN nodeaccess AS na ON na.nid = n.nid
LEFT JOIN field_data_field_date_posted AS fav ON fav.entity_id = n.nid
WHERE (na.gid IN(2) AND (n.status = '1') AND (n.type IN  ('article','blog', 'events', 'media', 'press_releases', 'expert_speak', 'feature', 'case_study', 'news', 'the_igtb_series', 'trend', 'white_paper')) )
GROUP BY n.nid  

ORDER BY ob ASC, pdate DESC

Fixed the order by date only base or group

UNION ALL - ORDER BY not working as expected ...?

Manually add a sort ordering for the selected item:

SELECT
  animation_id, 
  animation_name, 
  animation_group,
  CASE WHEN animation_id = '45' THEN 1 ELSE 0 END AS is_selected
FROM 
  animations
WHERE 
  animation_id = '45' OR (animation_id <> '45' AND active = true)
ORDER BY 
  is_selected DESC,
  animation_group, 
  animation_name

If you still want to keep your UNION for some reason:

SELECT 
  animation_id, 
  animation_name, 
  animation_group,
  1 AS is_selected
FROM 
  animations
WHERE 
  animation_id = '45'
UNION ALL -- If animation_id is unique, I can't see why you'd need a UNION ALL here, by the way 
SELECT 
  animation_id, 
  animation_name, 
  animation_group,
  0 AS is_selected
FROM 
  animations
WHERE
  animation_id <> '45' AND 
  active = true
ORDER BY
  is_selected DESC,
  animation_group, 
  animation_name

Also, assuming animation_id is a unique integer, 1) you don't need UNION ALL, as each row selected will be unique anyway, and 2) you don't need the quotes around the values, i.e. just animation_id = 45 will work, rather than animation_id = '45'.

Sort order of each select statement in a mysql union

Try this:

Select id,name from 
(
Select * from (
SELECT
  t.id,
  t.name,
  @rownum := @rownum + 1 as row_number
FROM
  test t
 cross join (select @rownum := 0) r
WHERE
  t.active=1
 order by t.name  ) tbl1

union all

select * from 
(
SELECT
  t.id,
  t.name,
  @rownum := @rownum + 1 as row_number
FROM
  test2 t
 cross join (select @rownum := 0) r
WHERE
  t.active=1
 order by t.id 
  ) tbl2
  ) x order by row_number

you should use union all

https://www.db-fiddle.com/f/dzBHKuzGmaQC8EmyuWcH2Y/2

mysql union changing order

Use of ORDER BY for individual SELECT statements implies nothing about the order in which the rows appear in the final result because UNION by default produces an unordered set of rows.1

It then gives this example of how to order the union result:

(SELECT a FROM t1 WHERE a=10 AND B=1)
UNION
(SELECT a FROM t2 WHERE a=11 AND B=2)
ORDER BY a LIMIT 10;

In your query you probably want to remove the order by in the individual sub-queries and add this after:

ORDER BY grade DESC, name, marks

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