SQL: finding differences between rows - mysql

Question

I want to count how many times each user has rows within '5' of eachother.
For example, Don - 501 and Don - 504 should be counted, while Don - 501 and Don - 1600 should not be counted.
Start:
Name value
_________ ______________
Don 1235
Don 6012
Don 6014
Don 6300
James 9000
James 9502
James 9600
Sarah 1110
Sarah 1111
Sarah 1112
Sarah 1500
Becca 0500
Becca 0508
Becca 0709
Finish:
Name difference_5
__________ _____________
Don 1
James 0
Sarah 2
Becca 0

Answer 1

Use the ABS() function, in conjunction with a self-join in a subquery:
So, something like:
SELECT name, COUNT(*) / 2 AS difference_5
FROM (
SELECT a.name name, ABS(a.value - b.value)
FROM tbl a JOIN tbl b USING(name)
WHERE ABS(a.value - b.value) BETWEEN 1 AND 5
) AS t GROUP BY name
edited as per Andreas' comment.

Answer 2

Assuming that each name -> value pair is unique, this will get you the count of times the value is within 5 per name:
SELECT a.name,
COUNT(b.name) / 2 AS difference_5
FROM tbl a
LEFT JOIN tbl b ON a.name = b.name AND
a.value <> b.value AND
ABS(a.value - b.value) <= 5
GROUP BY a.name
As you'll notice, we also have to exclude the pairs that are equal to themselves.
But if you wanted to count the number of times each name's values came within 5 of any value in the table, you can use:
SELECT a.name,
COUNT(b.name) / 2 AS difference_5
FROM tbl a
LEFT JOIN tbl b ON NOT (a.name = b.name AND a.value = b.value) AND
ABS(a.value - b.value) <= 5
GROUP BY a.name
See the SQLFiddle Demo for both solutions.

Answer 3

Because the OP also wants de zero counts, we'll need a self- left join. Extra logic is needed if one person has two exactly the same values, these should also be counted only once.
WITH cnts AS (
WITH pair AS (
SELECT t1.zname,t1.zvalue
FROM ztable t1
JOIN ztable t2
ON t1.zname = t2.zname
WHERE ( t1.zvalue < t2.zvalue
AND t1.zvalue >= t2.zvalue - 5 )
OR (t1.zvalue = t2.zvalue AND t1.ctid < t2.ctid)
)
SELECT DISTINCT zname
, COUNT(*) AS znumber
FROM pair
GROUP BY zname
)
, names AS (
SELECT distinct zname AS zname
FROM ztable
GROUP BY zname
)
SELECT n.zname
, COALESCE(c.znumber,0) AS znumber
FROM names n
LEFT JOIN cnts c ON n.zname = c.zname
;
RESULT:
DROP SCHEMA
CREATE SCHEMA
SET
CREATE TABLE
INSERT 0 14
zname | znumber
-------+---------
Sarah | 3
Don | 1
Becca | 0
James | 0
(4 rows)
NOTE: sorry for the CTE, I had not seen th mysql tag,I just liked the problem ;-)

Answer 4

SELECT
A.Name,
SUM(CASE WHEN (A.Value < B.Value) AND (A.Value >= B.Value - 5) THEN 1 ELSE 0 END) Difference_5
FROM
tbl A INNER JOIN
tbl B USING(Name)
GROUP BY
A.Name