Hi list,
I have a problem concerning two tables. Basically, I need a strict
"one on one join".
Simplyfied, the problem is as follows:
I need a check on two tables:
T1: containing four records, with the value of field id being 1, 2, 3, 4
T2, same structure, containing the records 1, 2, 3, 5 for field id.
I want to delete anything in table T1 which is not in T2. That is
simple:
delete t1 from t1 a left join t2 b
using(id)
where
b.id is not null;
However, Now my problem:
the problem is, that the id in both tables can contain duplicates.
When the tables have the following recs:
T1: field id: 1,1,2,3,4
T2: field id: 1,2,3,5
I want the delete command to delete ONE 1, the 2 and the 3, thus
resulting in a table T1 having left only two recrods, with id 1 and 4.
However, the delete matches both 1-records of T1 to the single 1-
record of T2, so both of them are deleted.
So, summarizing: I need a sort of "one on one join", which joins
only one single 1 in table T1 to a single 1 in table T2, and when
there's no 1 record left in T2, the other 1 in T1 should be
unmatched.
How can I do this?
Or if this is not possible, does somebody know some smart
workaround trick?
Thanks, rinke
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