Is there a simple way to LIMIT the GROUP BY results to the top 2. The following query returns all the results. Using 'LIMIT 2' reduces the overall list to the top 2 entries only.
select distinct(rating_name),
id_markets,
sum(rating_good) 'good',
sum(rating_neutral)'neutral',
sum(rating_bad) 'bad'
from ratings
where rating_year=year(curdate()) and rating_week= week(curdate(),1)
group by rating_name,id_markets
order by rating_name, sum(rating_good)
desc
Results in the following :-
poland 78 48 24 12 <- keep poland 1 15 5 0 <- keep poland 23 12 6 3 poland 2 5 0 0 poland 3 0 5 0 poland 4 0 0 5 ireland 1 9 3 0 <- keep ireland 2 3 0 0 <- keep ireland 3 0 3 0 ireland 4 0 0 3 france 12 24 12 6 <- keep france 1 3 1 0 <- keep france 231 1 0 0 france 2 1 0 0 france 4 0 0 1 france 3 0 1 0
Thanks Jon
As requested I have attached a copy of the table structure and some test data. My goal is to create a single view that has the top 2 results from each unique rating_name
CREATE TABLE `zzratings` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`id_markets` int(11) DEFAULT NULL,
`id_account` int(11) DEFAULT NULL,
`id_users` int(11) DEFAULT NULL,
`dateTime` timestamp NULL DEFAULT CURRENT_TIMESTAMP,
`rating_good` int(11) DEFAULT NULL,
`rating_neutral` int(11) DEFAULT NULL,
`rating_bad` int(11) DEFAULT NULL,
`rating_name` varchar(32) DEFAULT NULL,
`rating_year` smallint(4) DEFAULT NULL,
`rating_week` tinyint(4) DEFAULT NULL,
`cash_balance` decimal(9,6) DEFAULT NULL,
`cash_spend` decimal(9,6) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `rating_year` (`rating_year`),
KEY `rating_week` (`rating_week`),
KEY `rating_name` (`rating_name`)
) ENGINE=MyISAM AUTO_INCREMENT=2166690 DEFAULT CHARSET=latin1;
INSERT INTO `zzratings` (`id`,`id_markets`,`id_account`,`id_users`,`dateTime`,`rating_good`,`rating_neutral`,`rating_bad`,`rating_name`,`rating_year`,`rating_week`,`cash_balance`,`cash_spend`)
VALUES
(63741, 1, NULL, 100, NULL, 1, NULL, NULL, 'poland', 2010, 15, NULL, NULL),
(63742, 1, NULL, 101, NULL, 1, NULL, NULL, 'poland', 2010, 15, NULL, NULL),
(1, 2, NULL, 102, NULL, 1, NULL, NULL, 'poland', 2010, 15, NULL, NULL),
(63743, 3, NULL, 103, NULL, NULL, 1, NULL, 'poland', 2010, 15, NULL, NULL),
(63744, 4, NULL, 104, NULL, NULL, NULL, 1, 'poland', 2010, 15, NULL, NULL),
(63745, 1, NULL, 105, NULL, 1, NULL, NULL, 'poland', 2010, 15, NULL, NULL),
(63746, 1, NULL, 106, NULL, NULL, 1, NULL, 'poland', 2010, 15, NULL, NULL),
(63747, 5, NULL, 100, NULL, 1, NULL, NULL, 'ireland', 2010, 15, NULL, NULL),
(63748, 5, NULL, 101, NULL, 1, NULL, NULL, 'ireland', 2010, 15, NULL, NULL),
(63749, 2, NULL, 102, NULL, 1, NULL, NULL, 'ireland', 2010, 15, NULL, NULL),
(63750, 3, NULL, 103, NULL, NULL, 1, NULL, 'ireland', 2010, 15, NULL, NULL),
(63751, 4, NULL, 104, NULL, NULL, NULL, 1, 'ireland', 2010, 15, NULL, NULL),
(63752, 1, NULL, 105, NULL, 1, NULL, NULL, 'ireland', 2010, 15, NULL, NULL),
(63753, 1, NULL, 106, NULL, NULL, 1, NULL, 'ireland', 2010, 15, NULL, NULL),
(63754, 1, NULL, 100, NULL, 1, NULL, NULL, 'ireland', 2010, 15, NULL, NULL),
(63755, 1, NULL, 101, NULL, 1, NULL, NULL, 'ireland', 2010, 15, NULL, NULL),
(63756, 2, NULL, 102, NULL, 1, NULL, NULL, 'ireland', 2010, 15, NULL, NULL),
(63757, 34, NULL, 103, NULL, NULL, 1, NULL, 'ireland', 2010, 15, NULL, NULL),
(63758, 34, NULL, 104, NULL, NULL, NULL, 1, 'ireland', 2010, 15, NULL, NULL),
(63759, 34, NULL, 105, NULL, 1, NULL, NULL, 'ireland', 2010, 15, NULL, NULL),
(63760, 34, NULL, 106, NULL, NULL, 1, NULL, 'ireland', 2010, 15, NULL, NULL),
(63761, 21, NULL, 100, NULL, 1, NULL, NULL, 'ireland', 2010, 15, NULL, NULL),
(63762, 21, NULL, 101, NULL, 1, NULL, NULL, 'ireland', 2010, 15, NULL, NULL),
(63763, 21, NULL, 102, NULL, 1, NULL, NULL, 'ireland', 2010, 15, NULL, NULL),
(63764, 21, NULL, 103, NULL, NULL, 1, NULL, 'ireland', 2010, 15, NULL, NULL),
(63765, 4, NULL, 104, NULL, NULL, NULL, 1, 'ireland', 2010, 15, NULL, NULL),
(63766, 1, NULL, 105, NULL, 1, NULL, NULL, 'ireland', 2010, 15, NULL, NULL),
(63767, 1, NULL, 106, NULL, NULL, 1, NULL, 'ireland', 2010, 15, NULL, NULL),
(63768, 1, NULL, 100, NULL, 1, NULL, NULL, 'france', 2010, 15, NULL, NULL),
(63769, 1, NULL, 101, NULL, 1, NULL, NULL, 'france', 2010, 15, NULL, NULL),
(63770, 2, NULL, 102, NULL, 1, NULL, NULL, 'france', 2010, 15, NULL, NULL),
(63771, 3, NULL, 103, NULL, NULL, 1, NULL, 'france', 2010, 15, NULL, NULL),
(63772, 4, NULL, 104, NULL, NULL, NULL, 1, 'france', 2010, 15, NULL, NULL);
No, you can't LIMIT subqueries arbitrarily (you can do it to a limited extent in newer MySQLs, but not for 5 results per group). This is a groupwise-maximum type query, which is not trivial to do in SQL.
The ORDER BY clause goes after the FROM clause but before the LIMIT .
The MySQL LIMIT Clause The LIMIT clause is used to specify the number of records to return. The LIMIT clause is useful on large tables with thousands of records. Returning a large number of records can impact performance.
Limit Data Selections From a MySQL Database Assume we wish to select all records from 1 - 30 (inclusive) from a table called "Orders". The SQL query would then look like this: $sql = "SELECT * FROM Orders LIMIT 30"; When the SQL query above is run, it will return the first 30 records.
I don't think that there is a simple way in MySQL. One way to do this is by generating a row number for each row partitioned in groups by rating_name, and then only select the rows with row_number 2 or less. In most databases you could do this using something like:
SELECT * FROM (
SELECT
rating_name,
etc...,
ROW_NUMBER() OVER (PARTITION BY rating_name ORDER BY good) AS rn
FROM your_table
) T1
WHERE rn <= 2
Unfortunately, MySQL doesn't support the ROW_NUMBER
syntax. You can however simulate ROW_NUMBER
using variables:
SELECT
rating_name, id_markets, good, neutral, bad
FROM (
SELECT
*,
@rn := CASE WHEN @prev_rating_name = rating_name THEN @rn + 1 ELSE 1 END AS rn,
@prev_rating_name := rating_name
FROM (
SELECT
rating_name,
id_markets,
SUM(COALESCE(rating_good, 0)) AS good,
SUM(COALESCE(rating_neutral, 0)) AS neutral,
SUM(COALESCE(rating_bad, 0)) AS bad
FROM zzratings
WHERE rating_year = YEAR(CURDATE()) AND rating_week = WEEK(CURDATE(), 1)
GROUP BY rating_name, id_markets
) AS T1, (SELECT @prev_rating_name := '', @rn := 0) AS vars
ORDER BY rating_name, good DESC
) AS T2
WHERE rn <= 2
ORDER BY rating_name, good DESC
Result when run on your test data:
france 1 2 0 0 france 2 1 0 0 ireland 1 4 2 0 ireland 21 3 1 0 poland 1 3 1 0 poland 2 1 0 0
This is still possible via a single query, but it's a bit long, and there are some caveats, which I'll explain after the query. Though, they're not flaws in the query so much as some ambiguity in what "top two" means.
Here's the query:
SELECT ratings.* FROM
(SELECT rating_name,
id_markets,
sum(rating_good) 'good',
sum(rating_neutral)'neutral',
sum(rating_bad) 'bad'
FROM zzratings
WHERE rating_year=year(curdate()) AND rating_week = week(curdate(),1)
GROUP BY rating_name,id_markets) AS ratings
LEFT JOIN
(SELECT rating_name,
id_markets,
sum(rating_good) 'good',
sum(rating_neutral)'neutral',
sum(rating_bad) 'bad'
FROM zzratings
WHERE rating_year=year(curdate()) AND rating_week= week(curdate(),1)
GROUP BY rating_name,id_markets) AS ratings2
ON ratings2.good <= ratings.good AND
ratings2.id_markets <> ratings.id_markets AND
ratings2.rating_name = ratings.rating_name
LEFT JOIN
(SELECT rating_name,
id_markets,
sum(rating_good) 'good',
sum(rating_neutral)'neutral',
sum(rating_bad) 'bad'
FROM zzratings
WHERE rating_year=year(curdate()) AND rating_week= week(curdate(),1)
GROUP BY rating_name,id_markets) AS ratings3
ON ratings3.good >= ratings2.good AND
ratings3.id_markets <> ratings.id_markets AND
ratings3.id_markets <> ratings2.id_markets AND
ratings3.rating_name = ratings.rating_name
WHERE (ratings2.good IS NULL OR ratings3.good IS NULL) AND
ratings.good IS NOT NULL
ORDER BY ratings.rating_name, ratings.good DESC
The caveat is that if there is more than one id_market with the same "good" count for the same rating_name, then you will get more than two records. For example, if there are three ireland id_markets with a "good" count of 3, the highest, then how can you display the top two? You can't. So the query will show all three.
Also, if there were one count of "3", the highest, and two counts of "2", you couldn't show the top two, since you have a tie for second place, so the query shows all three.
The query will be simpler if you create a temporary table with the aggregate result set first, then work from that.
CREATE TEMPORARY TABLE temp_table
SELECT rating_name,
id_markets,
sum(rating_good) 'good',
sum(rating_neutral)'neutral',
sum(rating_bad) 'bad'
FROM zzratings
WHERE rating_year=year(curdate()) AND rating_week= week(curdate(),1;
SELECT ratings.*
FROM temp_table ratings
LEFT JOIN temp_table ratings2
ON ratings2.good <= ratings.good AND
ratings2.id_markets <> ratings.id_markets AND
ratings2.rating_name = ratings.rating_name
LEFT JOIN temp_table ratings3
ON ratings3.good >= ratings2.good AND
ratings3.id_markets <> ratings.id_markets AND
ratings3.id_markets <> ratings2.id_markets AND
ratings3.rating_name = ratings.rating_name
WHERE (ratings2.good IS NULL OR ratings3.good IS NULL) AND
ratings.good IS NOT NULL
ORDER BY ratings.rating_name, ratings.good DESC;
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