LAG

CREATE TABLE t1 (pk int primary key, a int, b int, c char(10), d decimal(10, 3), e real);

INSERT INTO t1 VALUES
 ( 1, 0, 1,    'one',    0.1,  0.001),
 ( 2, 0, 2,    'two',    0.2,  0.002),
 ( 3, 0, 3,    'three',  0.3,  0.003),
 ( 4, 1, 2,    'three',  0.4,  0.004),
 ( 5, 1, 1,    'two',    0.5,  0.005),
 ( 6, 1, 1,    'one',    0.6,  0.006),
 ( 7, 2, NULL, 'n_one',  0.5,  0.007),
 ( 8, 2, 1,    'n_two',  NULL, 0.008),
 ( 9, 2, 2,    NULL,     0.7,  0.009),
 (10, 2, 0,    'n_four', 0.8,  0.010),
 (11, 2, 10,   NULL,     0.9,  NULL);

SELECT pk, LAG(pk) OVER (ORDER BY pk) AS l,
  LAG(pk,1) OVER (ORDER BY pk) AS l1,
  LAG(pk,2) OVER (ORDER BY pk) AS l2,
  LAG(pk,0) OVER (ORDER BY pk) AS l0,
  LAG(pk,-1) OVER (ORDER BY pk) AS lm1,
  LAG(pk,-2) OVER (ORDER BY pk) AS lm2 
FROM t1;
+----+------+------+------+------+------+------+
| pk | l    | l1   | l2   | l0   | lm1  | lm2  |
+----+------+------+------+------+------+------+
|  1 | NULL | NULL | NULL |    1 |    2 |    3 |
|  2 |    1 |    1 | NULL |    2 |    3 |    4 |
|  3 |    2 |    2 |    1 |    3 |    4 |    5 |
|  4 |    3 |    3 |    2 |    4 |    5 |    6 |
|  5 |    4 |    4 |    3 |    5 |    6 |    7 |
|  6 |    5 |    5 |    4 |    6 |    7 |    8 |
|  7 |    6 |    6 |    5 |    7 |    8 |    9 |
|  8 |    7 |    7 |    6 |    8 |    9 |   10 |
|  9 |    8 |    8 |    7 |    9 |   10 |   11 |
| 10 |    9 |    9 |    8 |   10 |   11 | NULL |
| 11 |   10 |   10 |    9 |   11 | NULL | NULL |
+----+------+------+------+------+------+------+