How to select two fields of different rows? - mysql

Question

I have a table with this structure:
id int
min int
max int
I want to order it ascendently and select the max of the first row, and the min of the second one.
So I did this query, and before I get the values that I need:
select min, max
from mytable
order by min asc
limit 2;
Also I tried this:
select cm_max
from mytable
order by cm_min
limit 1
union
select cm_min
from mytable
order by cm_min
limit 1,1;
But does not work...
There is any way to select only the fields I'll use?

Answer 1

If you want your values to be returned in one row you can do
SELECT MIN(CASE WHEN rnum = 1 THEN cm_max END) cm_max,
MIN(CASE WHEN rnum = 2 THEN cm_min END) cm_min
FROM
(
SELECT id, cm_min, cm_max, #n := #n + 1 rnum
FROM medidas, (SELECT #n := 0) n
ORDER BY cm_min
LIMIT 2
) q
What it does it gets two records with your order condition and assigns a row number to each row in the inner select. Then in the outer select we pivot whose values using CASE and row numbers.
or
SELECT q1.cm_max, q2.cm_min
FROM
(
SELECT id, cm_min, cm_max
FROM medidas
ORDER BY cm_min
LIMIT 1
) q1 CROSS JOIN
(
SELECT id, cm_min, cm_max
FROM medidas
ORDER BY cm_min
LIMIT 1, 1
) q2
In this query we grab two records of interest in sub queries and use CROSS JOIN to join two records and output needed values.
Here is SQLFiddle demo for both queries

Answer 2

Change your limit to 1,1 to select just the 2nd record from that set:
select cm_max as 'value'
from medidas
order by cm_min
limit 1
union
select cm_min as 'value'
from medidas
order by cm_min
limit 1,1;
Not sure if MySQL will complain about mis-matching field names, so aliases may or may not be needed.