David T. Ashley wrote:
I have a table with two integer fields (call them p and q).
When I insert a record with a known p, I want to choose q to be one larger
than the largest q with that p.
What is the best and most efficient way to do this?
For example, let's say the table contains (p,q):
1,1
1,2
1,3
2,1
2,2
2,3
2.4
2,5
3,1
3,2
If I insert a new record with p=2, I would want to choose q to be 6. But if
I insert a record with p=3, I would want to choose q to be 3.
Is there any alternative to locking the table, querying for max q with the
desired p, then inserting?
insert into test1 set p = 2, q = (select max(q) + 1 from test1 as tmp
where p = 2)
Probably not very efficient, but it works.
-Stut
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http://stut.net/
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