Joining rows in Acces under specific conditions - ms-access

Question

I am working in access 2010 I have a table which has the following format:
ID BOORP BEGIN_DIEPTE EIND_DIEPTE TEXTUUR1
1 148000 0 10 ZK
2 148000 20 60 ZK
3 148000 60 80 MK
4 148000 80 110 MK
5 148000 110 130 ZK
6 148000 130 160 -
7 148000 160 220 ZZL
8 148000 220 250 -
9 148000 250 300 MK
10 148001 0 20 ZK
11 148001 20 40 -
12 148001 40 210 ZZL
13 148001 210 310 ZZL
What i want is to join certain rows which have the same texture under the following conditions:
1) rows must have the same BOORP in order to be merged
2) only consecutive rows may be merged
The result should look like this:
ID BOORP BEGIN_DIEPTE EIND_DIEPTE TEXTUUR1
1 148000 0 60 ZK
3 148000 60 110 MK
5 148000 110 130 ZK
6 148000 130 160 -
7 148000 160 220 ZZL
8 148000 220 250 -
9 148000 250 300 MK
10 148001 0 20 MK
11 148001 20 40 -
12 148001 40 310 ZZL
It is especially the 2nd condition i'm having problem with.
Any suggestions?

Answer 1

That's quite a complex task as an SQL-only solution.
If you want to do it in one query, you can use the following solution (tested on your sample data):
SELECT e.ID, e.BOORP, e.BEGIN_DIEPTE, e.EINDDIEPTE As EIND_DIEPTE, e.TEXTUUR1
FROM
(
SELECT a.ID, a.BOORP, a.BEGIN_DIEPTE, IIF(b.ID Is Null, a.EIND_DIEPTE, b.EIND_DIEPTE) AS EINDDIEPTE, a.TEXTUUR1, b.ID As IDJoined
FROM TestTable a
LEFT JOIN
(
SELECT c.*, (SELECT Max(d.ID) FROM TestTable d WHERE d.ID < c.ID) As PreviousID
FROM TestTable c
) As b
ON b.PreviousID = a.ID AND b.BOORP = a.BOORP AND a.TEXTUUR1 = b.TEXTUUR1
) AS e
WHERE e.ID NOT IN (
SELECT b.ID
FROM TestTable a
INNER JOIN
(
SELECT c.*, (SELECT Max(d.ID) FROM TestTable d WHERE d.ID < c.ID) As PreviousID
FROM TestTable c
) As b
ON b.PreviousID = a.ID AND b.BOORP = a.BOORP AND a.TEXTUUR1 = b.TEXTUUR1
)
It's quite a lot of subqueries, and a bit too much to explain in depth. Simply put, the most inner subquery (query b) LEFT JOINs on equal BOORP and TEXTUUR1 and where the ID is the previous ID, then the outer subquery (query e) takes the result, and removes all the entries that have been joined with another entry.
Note that this joins 2 entries together, not more than that. If you want to join more than 2 entries together, you can just run a similar query on the result of this one.