MySQL challenge using MIN and subquery - mysql

Question

My intent is to return a date value based on a selected year as well as a minimum date value based on a dataset that includes the complete dataset across all years. The query always returns the minimum date value in 2017. I want it to return the minimum start_date from the whole dataset.
What I get is for min_date_over_all_years
orgA 2017-10-09
orgB 2017-10-08
Required result for min_date_over_all_years is
orgA 2015-10-10
orgB 2014-10-09
Please see the attached fiddle for the example:
http://sqlfiddle.com/#!9/c0f74/9
The schema is:
CREATE TABLE IF NOT EXISTS `project` (
`project_id` int(11) NOT NULL AUTO_INCREMENT,
`p_name` varchar(10) NOT NULL,
`start_date` DATE NOT NULL,
`organisation_id` int(11) NOT NULL,
PRIMARY KEY (`project_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=6 ;
INSERT INTO `project` (`project_id`, `p_name`,
`start_date`, `organisation_id`)
VALUES
(1, 'testP1', '2017-10-09', 1),
(2, 'testP2', '2016-10-10', 1),
(3, 'testP3', '2015-10-10', 1),
(4, 'testP4', '2017-10-10', 2),
(5, 'testP5', '2014-10-10', 2),
(6, 'testP6', '2017-10-10', 1),
(7, 'testP7', '2016-10-10', 1),
(8, 'testP8', '2015-10-10', 1),
(9, 'testP9', '2017-10-08', 2),
(10, 'testP10', '2014-10-09', 2);
CREATE TABLE IF NOT EXISTS `organisation` (`organisation_id` int(11) NOT NULL AUTO_INCREMENT,
`org_name` varchar(10) NOT NULL,
PRIMARY KEY (`organisation_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=6 ;
INSERT INTO `organisation` (`organisation_id`, `org_name`
)
VALUES
(1, 'orgA'),
(2, 'orgB');
AND the query I have tried (along with simpler subquery and Case versions) is:
SELECT o.org_name, MIN(p.start_date) AS min_date_2017, YEAR(p.start_date) AS year_selected,
(SELECT MIN(p.start_date) FROM project p2
INNER JOIN organisation o2 ON o2.organisation_id = p2.organisation_id
WHERE p2.organisation_id = o.organisation_id
GROUP BY o2.organisation_id) AS min_date_over_all_years
FROM organisation o
INNER JOIN project p on p.organisation_id = o.organisation_id
WHERE YEAR(p.start_date)=2017
GROUP BY o.organisation_id

Answer 1

You can't put a subquery that returns multiple rows in the SELECT list; when a subquery is being used as an expression, it has to return a single row with a single column.
You don't need a separate query.
SELECT o.org_name,
MIN(IF(YEAR(p.start_date) = 2017, p.start_date, NULL)) AS min_date_2017,
2017 AS year_selected,
MIN(p.start_date) AS min_date_over_all_years
FROM organisation AS o
INNER JOIN project AS p ON p.organisation_id = o.organisation_id
GROUP BY o.organisation_id
You can also join with a subquery that gets the overall data.
SELECT o.org_name, MIN(p.start_date) AS min_date_2017, YEAR(p.start_date) AS year_selected, overall.start_date AS min_date_over_all_years
FROM organisation o
INNER JOIN project p on p.organisation_id = o.organisation_id
INNER JOIN (
SELECT organisation_id, MIN(start_date) AS start_date
FROM project
GROUP BY organisation_id) AS overall ON o.organisation_id = overall.organisation_id
WHERE YEAR(p.start_date)=2017
GROUP BY o.organisation_id