Question

I have a table called crewWork as follows :

CREATE TABLE crewWork( 
       FloorNumber int, AptNumber int, WorkType int, simTime int )

After the table was populated, I need to know how many times a change in apt occurred and how many times a change in floor occurred. Usually I expect to find 10 rows on each apt and 40-50 on each floor.
I could just write a scalar function for that, but I was wondering if there’s any way to do that in t-SQL without having to write scalar functions.

Thanks

The data will look like this:

FloorNumber  AptNumber    WorkType      simTime  
1            1            12            10  
1            1            12            25  
1            1            13            35  
1            1            13            47  
1            2            12            52  
1            2            12            59  
1            2            13            68  
1            1            14            75  
1            4            12            79  
1            4            12            89  
1            4            13            92  
1            4            14            105  
1            3            12            115  
1            3            13            129  
1            3            14            138  
2            1            12            142  
2            1            12            150  
2            1            14            168  
2            1            14            171  
2            3            12            180  
2            3            13            190  
2            3            13            200  
2            3            14            205  
3            3            14            216  
3            4            12            228  
3            4            12            231  
3            4            14            249  
3            4            13            260  
3            1            12            280  
3            1            13            295  
2            1            14            315  
2            2            12            328  
2            2            14            346  

I need the information for a report, I don’t need to store it anywhere.

Answer 1

If I am not missing anything, you could use the following method to find the number of changes:

• determine groups of sequential rows with identical values;

• count those groups;

• subtract 1.

Apply the method individually for AptNumber and for FloorNumber.

The groups could be determined like in this answer, only there’s isn’t a Seq column in your case. Instead, another ROW_NUMBER() expression could be used. Here’s an approximate solution:

;
WITH marked AS (
  SELECT
    FloorGroup = ROW_NUMBER() OVER (                         ORDER BY simTime)
               - ROW_NUMBER() OVER (PARTITION BY FloorNumber ORDER BY simTime),

    AptGroup   = ROW_NUMBER() OVER (                         ORDER BY simTime)
               - ROW_NUMBER() OVER (PARTITION BY AptNumber   ORDER BY simTime)
  FROM crewWork
)
SELECT
  FloorChanges = COUNT(DISTINCT FloorGroup) - 1,
  AptChanges   = COUNT(DISTINCT AptGroup)   - 1
FROM marked

(I’m assuming here that the simTime column defines the timeline of changes.)

---

UPDATE

Below is a table that shows how the distinct groups are obtained for AptNumber.

AptNumber  RN  RN_Apt  AptGroup (= RN - RN_Apt)
---------  --  ------  ---------
1          1   1       0
1          2   2       0
1          3   3       0
1          4   4       0
2          5   1       4
2          6   2       4
2          7   3       4
1          8   5   =>  3
4          9   1       8
4          10  2       8
4          11  3       8
4          12  4       8
3          13  1       12
3          14  2       12
3          15  3       12
1          16  6       10
…          …   …       …

Here RN is a pseudo-column that stands for ROW_NUMBER() OVER (ORDER BY simTime). You can see that this is just a sequence of rankings starting from 1.

Another pseudo-column, RN_Apt contains values produces by the other ROW_NUMBER, namely ROW_NUMBER() OVER (PARTITION BY AptNumber ORDER BY simTime). It contains rankings within individual groups of identical AptNumber values. You can see that, for a newly encountered value, the sequence starts over, and for a recurring one, it continues where it stopped last time.

You can also see from the table that if we subtract RN from RN_Apt (could be the other way round, doesn’t matter in this situation), we get the value that uniquely identifies every distinct group of same AptNumber values. You might as well call that value a group ID.

So, now that we’ve got these IDs, it only remains for us to count them (count distinct values, of course). That will be the number of groups, and the number of changes is one less (assuming the first group is not counted as a change).