Select a single result from groups by the min of two values - mysql

Question

I have a table that looks like this:
+----+-------+---------+--------+--------+
| id | meta1 | meta2 | value1 | value2 |
+----+-------+---------+--------+--------+
| 1 | foo | bar | 0.1 | 0.01 |
| 1 | baz | quux | 0.2 | 0.01 |
| 1 | lorem | ipsum | 0.1 | 0.05 |
| 2 | dolor | sit | 0.2 | 0.02 |
| 2 | amet | eos | 0.3 | 0.02 |
| 3 | clita | corpora | 0.5 | 0.03 |
+----+-------+---------+--------+--------+
I am trying to extract one (complete) row for each id with the lowest value1 and in the case that there are equal value1s, falling back to the lowest value2.
The query should result in a result set like this:
+----+-------+---------+--------+--------+
| id | meta1 | meta2 | value1 | VALUE2 |
+----+-------+---------+--------+--------+
| 1 | foo | bar | 0.1 | 0.01 |
| 2 | dolor | sit | 0.2 | 0.02 |
| 3 | clita | corpora | 0.5 | 0.03 |
+----+-------+---------+--------+--------+
I started by attempting the following query:
SELECT
t1.*
FROM
test t1
INNER JOIN
(SELECT
id, MIN(value1) minValue1
FROM
test
GROUP BY id) t2 ON t1.id = t2.id
AND t1.value1 = t2.minValue1;
But this doesn't 'break the tie' for id '1' and I end up with two of those records. I have tried adding HAVING clauses and additional subqueries and am lost beyond this initial step. Help much appreciated.

Answer 1

You want all records for which no better record (ie. with lower value1 or same value1 and lower value2) exists:
select *
from mytable
where not exists
(
select *
from mytable better
where better.id = mytable.id
and
(
better.value1 < mytable.value1
or
(better.value1 = mytable.value1 and better.value2 < mytable.value2)
)
);

Answer 2

You can use not exists:
SELECT t.*
FROM test t
WHERE NOT EXISTS (SELECT 1
FROM test t2
WHERE t2.id = t.id AND
(t2.value1 < t.value1 OR
(t2.value1 = t.value1 and t2.value2 < t.value2) )
);
An alternative method is to use variables:
select t.*
from (select t.*,
(#rn := if(#i = id, #rn + 1,
if(#i := id, 1, 1)
)
) as rn
from test t cross join
(select #rn := 0, #i := -1) params
order by id, value1, value2
) t
where rn = 1;

Answer 3

Consider the following...
DROP TABLE IF EXISTS my_table;
CREATE TABLE my_table
(id INT NOT NULL
,meta1 VARCHAR(12)
,meta2 VARCHAR(12)
,value1 DECIMAL(5,2)
,value2 DECIMAL(5,2)
);
INSERT INTO my_table VALUES
(1 ,'foo','bar',0.1,0.09),
(1 ,'baz','quux',0.2,0.08),
(1 ,'lorem','ipsum',0.1,0.07),
(2 ,'dolor','sit',0.2,0.06),
(2 ,'amet','eos',0.3,0.05),
(3 ,'clita','corpora',0.5,0.04);
SELECT a.*
FROM my_table a
JOIN
( SELECT x.id
, x.value1
, MIN(x.value2) min_value2
FROM my_table x
JOIN
( SELECT id
, MIN(value1) min_value1
FROM my_table
GROUP
BY id
) y
ON y.id = x.id
AND y.min_value1 = x.value1
GROUP
BY x.id
, x.value1
) b
ON b.id = a.id
AND b.value1 = a.value1
AND b.min_value2 = a.value2;
+----+-------+---------+--------+--------+
| id | meta1 | meta2 | value1 | value2 |
+----+-------+---------+--------+--------+
| 1 | lorem | ipsum | 0.10 | 0.07 |
| 2 | dolor | sit | 0.20 | 0.06 |
| 3 | clita | corpora | 0.50 | 0.04 |
+----+-------+---------+--------+--------+
you can extend this indefinitely, but at some point an laternative solution may become easier to manage...
DROP TABLE IF EXISTS my_table;
CREATE TABLE my_table
(id INT NOT NULL
,meta1 VARCHAR(12)
,meta2 VARCHAR(12)
,value1 DECIMAL(5,2)
,value2 DECIMAL(5,2)
);
INSERT INTO my_table VALUES
(1 ,'foo' ,'bar' ,0.1,0.09),
(1 ,'baz' ,'quux' ,0.2,0.08),
(1 ,'lorem','ipsum' ,0.1,0.07),
(2 ,'dolor','sit' ,0.2,0.06),
(2 ,'amet' ,'eos' ,0.3,0.05),
(3 ,'clita','corpora',0.5,0.04),
(1 ,'bar' ,'foo' ,0.1,0.07);
SELECT a.*
FROM my_table a
JOIN
(
SELECT q.id
, q.value1
, q.value2
, MIN(q.meta1) min_meta1
FROM my_table q
JOIN
(
SELECT x.id
, x.value1
, MIN(x.value2) min_value2
FROM my_table x
JOIN
( SELECT id
, MIN(value1) min_value1
FROM my_table
GROUP
BY id
) y
ON y.id = x.id
AND y.min_value1 = x.value1
GROUP
BY x.id
, x.value1
) r
ON r.id = q.id
AND r.value1 = q.value1
AND r.min_value2 = q.value2
GROUP
BY q.id
, q.value1
, q.value2
) b
ON b.id = a.id
AND b.value1 = a.value1
AND b.value2 = a.value2
AND b.min_meta1 = a.meta1;
+----+-------+---------+--------+--------+
| id | meta1 | meta2 | value1 | value2 |
+----+-------+---------+--------+--------+
| 2 | dolor | sit | 0.20 | 0.06 |
| 3 | clita | corpora | 0.50 | 0.04 |
| 1 | bar | foo | 0.10 | 0.07 |
+----+-------+---------+--------+--------+