SQL - How to Order By in UNION query
Put a UNION ALL
in a derived table. To keep duplicate elimination, do select distinct
and also add a NOT EXISTS
to second select to avoid returning same person twice if found in both tables:
select name, surname
from
(
select distinct name, surname, 1 as tno
from table1
union all
select distinct name, surname, 2 as tno
from table2 t2
where not exists (select * from table1 t1
where t2.name = t1.name
and t2.surname = t1.surname)
) dt
order by tno, surname, name
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
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.
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
Using different order by with union
This should work:
SELECT *
FROM (SELECT TOP 10 A.*, 0 AS Ordinal
FROM A
ORDER BY [Price]) AS A1
UNION ALL
SELECT *
FROM (SELECT TOP 3 A.*, 1 AS Ordinal
FROM A
ORDER BY [Name]) AS A2
ORDER BY Ordinal
From MSDN:
In a query that uses UNION, EXCEPT, or INTERSECT operators, ORDER BY
is allowed only at the end of the statement. This restriction applies
only to when you specify UNION, EXCEPT and INTERSECT in a top-level
query and not in a subquery.
Edited: to force the order you need to apply an ORDER BY
to the outer query. I've added a constant value column to both queries.
How to use order by with union all in sql?
SELECT *
FROM
(
SELECT * FROM TABLE_A
UNION ALL
SELECT * FROM TABLE_B
) dum
-- ORDER BY .....
but if you want to have all records from Table_A
on the top of the result list, the you can add user define value which you can use for ordering,
SELECT *
FROM
(
SELECT *, 1 sortby FROM TABLE_A
UNION ALL
SELECT *, 2 sortby FROM TABLE_B
) dum
ORDER BY sortby
SQL: how to use UNION and order by a specific select?
Using @Adrian tips, I found a solution:
I'm using GROUP BY and COUNT.
I tried to use DISTINCT with ORDER BY but I'm getting error message: "not a SELECTed expression"
select id from
(
SELECT id FROM a -- returns 1,4,2,3
UNION ALL -- changed to ALL
SELECT id FROM b -- returns 2,1
)
GROUP BY id ORDER BY count(id);
Thanks Adrian and this blog.
SELECT TOP N with UNION and ORDER BY
A Union query works thus: execute the queries, then apply the order by clause. So with
SELECT TOP 5 [ID], [Description], [Inactive]
FROM #T1
UNION ALL
SELECT TOP 5 [ID], [Description], [Inactive]
FROM #T2
ORDER BY [Inactive], [Description];
you select five arbitrarily chosen records from #T1 plus five arbitrarily chosen records from #T2 and then you order these. So you need subqueries or with clauses. E.g.:
SELECT * FROM
(
(
SELECT TOP 5 [ID], [Description], [Inactive]
FROM #T1
ORDER BY [Inactive], [Description]
)
UNION ALL
(
SELECT TOP 5 [ID], [Description], [Inactive]
FROM #T2
ORDER BY [Inactive], [Description]
)
) t;
So your workaround is not a workaround at all, but the proper query.
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