Grouping by column and rows - sql

Question

I have a table like this:
+----+--------------+--------+----------+
| id | name | weight | some_key |
+----+--------------+--------+----------+
| 1 | strawberries | 12 | 1 |
| 2 | blueberries | 7 | 1 |
| 3 | elderberries | 0 | 1 |
| 4 | cranberries | 8 | 2 |
| 5 | raspberries | 18 | 2 |
+----+--------------+--------+----------+
I'm looking for a generic request that would get me all berries where there are three entries with the same 'some_key' and one of the entries (within those three entries belonging to the same some_key) has the weight = 0
in case of the sample table, expected output would be:
1 strawberries
2 blueberries
3 cranberries

Answer 1

As you want to include non-grouped columns, I would approach this with window functions:
select id, name
from (
select id,
name,
count(*) over w as key_count,
count(*) filter (where weight = 0) over w as num_zero_weight
from fruits
window w as (partition by some_key)
) x
where x.key_count = 3
and x.num_zero_weight >= 1
The count(*) over w counts the number of rows in that group (= partition) and the count(*) filter (where weight = 0) over w counts how many of those have a weight of zero.
The window w as ... avoids repeating the same partition by clause for the window functions.
Online example: https://rextester.com/SGWFI49589

Answer 2

Try this-
SELECT some_key,
SUM(weight) --Sample aggregations on column
FROM your_table
GROUP BY some_key
HAVING COUNT(*) = 3 -- If you wants at least 3 then use >=3
AND SUM(CASE WHEN weight = 0 THEN 1 ELSE 0 END) >= 1
As per your edited question, you can try this below-
SELECT id, name
FROM your_table
WHERE some_key IN (
SELECT some_key
FROM your_table
GROUP BY some_key
HAVING COUNT(*) = 3 -- If you wants at least 3 then use >=3
AND SUM(CASE WHEN weight = 0 THEN 1 ELSE 0 END) >= 1
)

Answer 3

Try doing this.
Table structure and sample data
CREATE TABLE tmp (
id int,
name varchar(50),
weight int,
some_key int
);
INSERT INTO tmp
VALUES
('1', 'strawberries', '12', '1'),
('2', 'blueberries', '7', '1'),
('3', 'elderberries', '0', '1'),
('4', 'cranberries', '8', '2'),
('5', 'raspberries', '18', '2');
Query
SELECT t1.*
FROM tmp t1
INNER JOIN (SELECT some_key
FROM tmp
GROUP BY some_key
HAVING Count(some_key) >= 3
AND Min(Abs(weight)) = 0) t2
ON t1.some_key = t2.some_key;
Output
+-----+---------------+---------+----------+
| id | name | weight | some_key |
+-----+---------------+---------+----------+
| 1 | strawberries | 12 | 1 |
| 2 | blueberries | 7 | 1 |
| 3 | elderberries | 0 | 1 |
+-----+---------------+---------+----------+
Online Demo: http://sqlfiddle.com/#!15/70cca/26/0
Thank you, #mkRabbani for reminding me about the negative values.
Further reading
- ABS() Function - Link01, Link02
- HAVING Clause - Link01, Link02