How to simplify sequence data in MySQL? - mysql

Question

I have asked a question on How to get temporal sequence by mysql before. There I want to get a simplified sequence with the latest date.
Now I want to get the start date and end date of each sequence. Suppose that the table is still like this:
ID DATE STATUS
1 0106 A
1 0107 A
1 0112 A
1 0130 B
1 0201 A
2 0102 C
2 0107 C
and I want to get the result like this:
ID START_DATE END_DATE STATUS
1 0106 0112 A
1 0130 0130 B
1 0201 0201 A
2 0102 0107 C
I tried to adapt the answer of former question to it though but failed. I am wondering how I can realize it.

Answer 1

Given this
SELECT * FROM T;
+------+------+--------+
| ID | DATE | STATUS |
+------+------+--------+
| 1 | 106 | A |
| 1 | 107 | A |
| 1 | 112 | A |
| 1 | 130 | B |
| 1 | 201 | A |
| 2 | 102 | C |
| 2 | 107 | C |
+------+------+--------+
It's quite straightforward to allocate a block and seqno using this
SELECT T.ID,T.DATE,T.STATUS,
IF(STATUS <> #PREVS,#RN:=#RN+1,#RN:=#RN) RNBLOCK ,
IF(STATUS = #PREVS,#RN2:=#RN2+1,#RN2:=1) RNSEQ ,
#PREVS:=STATUS PSTATUS
FROM (SELECT #RN:=1) RNBLOCK, (SELECT #RN2:=0) RNSEQ,(SELECT #PREVS:=NULL) P, T
To give this
+------+------+--------+---------+-------+---------+
| ID | DATE | STATUS | RNBLOCK | RNSEQ | PSTATUS |
+------+------+--------+---------+-------+---------+
| 1 | 106 | A | 1 | 1 | A |
| 1 | 107 | A | 1 | 2 | A |
| 1 | 112 | A | 1 | 3 | A |
| 1 | 130 | B | 2 | 1 | B |
| 1 | 201 | A | 3 | 1 | A |
| 2 | 102 | C | 4 | 1 | C |
| 2 | 107 | C | 4 | 2 | C |
+------+------+--------+---------+-------+---------+
So now we have isolated the blocks and know the min seq no (1) and the max seqno and we can push them into a table
drop table t1;
CREATE TABLE `t1` (
`ID` INT(11) NULL DEFAULT NULL,
`DATE` INT(11) NULL DEFAULT NULL,
`STATUS` VARCHAR(1) NULL DEFAULT NULL,
`rnblock` int null default null,
`rnseq` int null default null,
`pstatus` VARCHAR(1) NULL DEFAULT NULL
)
COLLATE='latin1_swedish_ci'
ENGINE=InnoDB
;
and create a simple min max join
SELECT T2.ID,T2.DATE,T3.DATE,T2.STATUS FROM
(
SELECT T1.RNBLOCK,MAX(T1.RNSEQ) MAXSEQ
FROM T1
GROUP BY RNBLOCK
) S
JOIN T1 T2 ON T2.RNBLOCK = S.RNBLOCK AND T2.RNSEQ = 1
JOIN T1 T3 ON T3.RNBLOCK = S.RNBLOCK AND T3.RNSEQ = S.MAXSEQ
to get this
+------+------+------+--------+
| ID | DATE | DATE | STATUS |
+------+------+------+--------+
| 1 | 106 | 112 | A |
| 1 | 130 | 130 | B |
| 1 | 201 | 201 | A |
| 2 | 102 | 107 | C |
+------+------+------+--------+
The downside is that you have to create a table to make it work.
Or you could use this rather ungainly code which does not use an intermediate table
select u.id,u.date,v.date,u.status from
(
select s.rnblock,s.status,min(s.rnseq) minseq,max(s.rnseq) maxseq
from
(
SELECT T.ID,T.DATE,T.STATUS,
IF(STATUS <> #PREVS,#RN:=#RN+1,#RN:=#RN) RNBLOCK ,
IF(STATUS = #PREVS,#RN2:=#RN2+1,#RN2:=1) RNSEQ ,
#PREVS:=STATUS PSTATUS
FROM (SELECT #RN:=1) RNBLOCK, (SELECT #RN2:=0) RNSEQ,(SELECT #PREVS:=NULL) P, T
) s
group by s.rnblock,s.status
) T
join
(SELECT T.ID,T.DATE,T.STATUS,
IF(STATUS <> #PREVS2,#RN3:=#RN3+1,#RN3:=#RN3) RNBLOCK ,
IF(STATUS = #PREVS2,#RN4:=#RN4+1,#RN4:=1) RNSEQ ,
#PREVS2:=STATUS PSTATUS
FROM (SELECT #RN3:=1) RNBLOCK, (SELECT #RN4:=0) RNSEQ,(SELECT #PREVS2:=NULL) P, T
) u on u.rnblock = t.rnblock and u.rnseq = minseq
join
(SELECT T.ID,T.DATE,T.STATUS,
IF(STATUS <> #PREVS3,#RN5:=#RN5+1,#RN5:=#RN5) RNBLOCK ,
IF(STATUS = #PREVS3,#RN6:=#RN6+1,#RN6:=1) RNSEQ ,
#PREVS3:=STATUS PSTATUS
FROM (SELECT #RN5:=1) RNBLOCK, (SELECT #RN6:=0) RNSEQ,(SELECT #PREVS3:=NULL) P, T
) v on v.rnblock = t.rnblock and v.rnseq = maxseq

Answer 2

Oh I have just thought out a method though it seems very stupid. The method is just executing the code from How to get temporal sequence by mysql twice(by different order) and join these two tables.