How to calculate mysql query, a difference between the two closest rows in the column?

SELECT partnum, LAG(partnum) OVER w AS 'prev_partnum', partnum - LAG(partnum) OVER w AS 'diff' FROM nspcl WINDOW w AS (ORDER BY id);

SELECT t2.partnum p2, t1.partnum p1, t2.partnum - t1.partnum res FROM nspcl t1 Nspcl INNER JOIN t2 ON t1.id = (t2.id - 1)

SELECT t1.num, t2.num, t2.num is a t1.num FROM ( SELECT num, ROW_NUMBER() OVER(ORDER BY num) AS rn FROM table ) AS t1 LEFT JOIN ( SELECT num, ROW_NUMBER() OVER(ORDER BY num) AS rn FROM table ) AS t2 ON t1.rn=t2.rn-1

"two ends, two rings, in the middle of the stud" - "points to the boob nailed"