Get next and previous primary keys that match a pattern - mysql

Question

I have a database similar to the following...
ID ! Value
...
654 ! Blue
656 ! Green
659 ! Blue
665 ! Blue
...
I have the value of a numerical primary key. I'm wanting to do a query that pulls the previous and next primary keys that match a pattern.
For example, I have ID 659, I want to do something like
SELECT NEXT, PREV FROM TABLE WHERE VALUE = 'Blue';
And I'm trying to do it efficiently instead of fetching the whole table.

Answer 1

1 row and 2 columns:
SELECT
(SELECT ID FROM test WHERE ID < 659 AND Value = 'Blue' ORDER BY ID DESC LIMIT 1) AS PREV,
(SELECT ID FROM test WHERE ID > 659 AND Value = 'Blue' ORDER BY ID ASC LIMIT 1) AS NEXT;
2 rows and 1 column:
(SELECT ID AS PREV FROM test WHERE ID < 659 AND Value = 'Blue' ORDER BY ID DESC LIMIT 1)
UNION
(SELECT ID AS NEXT FROM test WHERE ID > 659 AND Value = 'Blue' ORDER BY ID ASC LIMIT 1);

Answer 2

DROP TABLE IF EXISTS T;
CREATE TABLE T (ID INT PRIMARY KEY,VAL VARCHAR(10));
INSERT INTO T (ID,VAL) VALUES (654,'BLUE'),(656,'GREEN'),(659,'BLUE'),(665,'BLUE');
SELECT CURRENT.ID CURRENTID,CURRENT.VAL,
(SELECT MIN(ID) FROM T NEXT WHERE NEXT.ID > CURRENT.ID AND NEXT.VAL = CURRENT.VAL) NEXT,
(SELECT MAX(ID) FROM T PREV WHERE PREV.ID < CURRENT.ID AND PREV.VAL = CURRENT.VAL) PREV
FROM T CURRENT;
+-----------+-------+------+------+
| CURRENTID | VAL | NEXT | PREV |
+-----------+-------+------+------+
| 654 | BLUE | 659 | NULL |
| 656 | GREEN | NULL | NULL |
| 659 | BLUE | 665 | 654 |
| 665 | BLUE | NULL | 659 |
+-----------+-------+------+------+
4 rows in set (0.00 sec)
Or less elegantly (can't say about performance)
SELECT CURRENT.ID CURRENTID,CURRENT.VAL,
NEXT.ID NEXTID,PREV.ID PREVID
FROM
(
SELECT T.ID, T.VAL, IF(T.VAL<>#P,#RN:=1,#RN:=#RN+1) RN, #P:=T.VAL
FROM T,(SELECT #RN:=0,#P:=0) R
ORDER BY T.VAL,T.ID
) CURRENT
LEFT JOIN
(
SELECT T.ID, T.VAL, IF(T.VAL<>#P1,#RN1:=1,#RN1:=#RN1+1) RN1, #P1:=T.VAL
FROM T,(SELECT #RN1:=0,#P1:=0) R1
ORDER BY T.VAL,T.ID
) NEXT ON NEXT.VAL = CURRENT.VAL AND NEXT.RN1 = CURRENT.RN + 1
LEFT JOIN
(
SELECT T.ID, T.VAL, IF(T.VAL<>#P2,#RN2:=1,#RN2:=#RN2+1) RN2, #P2:=T.VAL
FROM T,(SELECT #RN2:=0,#P2:=0) R2
ORDER BY T.VAL,T.ID
) PREV ON PREV.VAL = CURRENT.VAL AND PREV.RN2 = CURRENT.RN - 1
;
+-----------+-------+--------+--------+
| CURRENTID | VAL | NEXTID | PREVID |
+-----------+-------+--------+--------+
| 654 | BLUE | 659 | NULL |
| 659 | BLUE | 665 | 654 |
| 665 | BLUE | NULL | 659 |
| 656 | GREEN | NULL | NULL |
+-----------+-------+--------+--------+
4 rows in set (0.00 sec)