Question

我有一个类似于以下的数据库......

ID    ! Value 
...
654 ! Blue
656 ! Green
659 ! Blue
665 ! Blue
...

我有一个数字主键的值。我想要执行一个查询来提取与模式匹配的上一个和下一个主键。

例如，我有ID 659，我想做类似

的事情

SELECT NEXT, PREV FROM TABLE WHERE VALUE = 'Blue';

我试图有效地做而不是拿整张桌子。

Answer 1

1行2列：

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行1列：

(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)

或不那么优雅（不能说性能）

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)

获取与模式匹配的下一个和上一个主键

2 个答案: