Question

I’m trying to return all values of foo joined with the max values of bar where foo.val > bar.val

CREATE TABLE `foo` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `val` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
);

CREATE TABLE `bar` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `val` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
);

insert into foo (val) values (3), (5), (7), (10);
insert into bar (val) values (1), (1), (2), (3), (4), (5), (6), (7), (8), (20);

The expected output would be like:

+--------+---------+------------------------+
| foo.id | foo.val | max(bar.val) < foo.val |
+--------+---------+------------------------+
|  1     | 3       | 2                      |
|  2     | 5       | 4                      |
|  3     | 7       | 6                      |
|  4     | 10      | 8                      |
+--------+---------+------------------------+

Can this be done with a single query rather than looping through in code-land?

SELECT max(val) from bar where val < 3;
SELECT max(val) from bar where val < 5;
SELECT max(val) from bar where val < 7;
SELECT max(val) from bar where val < 10;

Anyone have any ideas on this?

Fiddle is here if anyone wants to try it http://sqlfiddle.com/#!2/de0f9/7

Thanks in advance.

Answer 1

select  foo.id,
        foo.val,
        (select MAX(bar.val) from bar where bar.val < foo.val) as barval
from foo

It will return null in no smaller value is find in bar, maybe use coalesce if you need a value.