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How to update foreign key in tbl B based on tbl A?

Author

Topic

raffiq_eddy
Starting Member

12 Posts

Posted - 2007-08-09 : 04:54:39

Hi SQL Expert,

I want to update the foreign key in table B according to table A, please help me

E.g.


Table A
PK1	PK2
1	1
1	2
1	3


Table B (before)
PK	FK1	FK2
A	1	1
B	1	4
C	1	5

I want the result as following...


Table B (after)
PK	FK1	FK2
A	1	1
B	1	2*
C	1	3*

* changes only apply to this data

Is this possible, can this be done using only 1 sql statement?

TIA

nr
SQLTeam MVY

12543 Posts

Posted - 2007-08-09 : 05:16:34

update TableB
set FK2 = at.PK2
from
TableB b
join
(select PK, FK1, FK2, seq = (select count(*) from TableB b2 where b2.FK1 = b.FK1 and b2.FK2 <= b.FK2) from TableB b) bt
on b.PK = bt.PK
(select PK1, PK2, seq = (select count(*) from TableA a2 where a2.PK1 = a.PK1 and a2.PK2 <= a.PK2) from TableA a) at
join bt
on at.PK1 = bt.FK1
and at.seq = bt.seq

==========================================
Cursors are useful if you don't know sql.
DTS can be used in a similar way.
Beer is not cold and it isn't fizzy.

raffiq_eddy
Starting Member

12 Posts

Posted - 2007-08-10 : 22:23:35

thanks for prompt reply nr!

sorry for the late reply from me though

I'll try ur solution now

quote:
Originally posted by nr

update TableB
set FK2 = at.PK2
from
TableB b
join
(select PK, FK1, FK2, seq = (select count(*) from TableB b2 where b2.FK1 = b.FK1 and b2.FK2 <= b.FK2) from TableB b) bt
on b.PK = bt.PK
(select PK1, PK2, seq = (select count(*) from TableA a2 where a2.PK1 = a.PK1 and a2.PK2 <= a.PK2) from TableA a) at
join bt
on at.PK1 = bt.FK1
and at.seq = bt.seq

raffiq_eddy
Starting Member

12 Posts

Posted - 2007-08-11 : 02:40:31

I tried to run the script given but query analyzer return this error:

Line 7: Incorrect syntax near 'at'.

which highlighted this line...

(select PK1, PK2, seq = (select count(*) from TableA a2 where a2.PK1 = a.PK1 and a2.PK2 <= a.PK2) from TableA a) at

quote:
Originally posted by nr

update TableB
set FK2 = at.PK2
from
TableB b
join
(select PK, FK1, FK2, seq = (select count(*) from TableB b2 where b2.FK1 = b.FK1 and b2.FK2 <= b.FK2) from TableB b) bt
on b.PK = bt.PK
(select PK1, PK2, seq = (select count(*) from TableA a2 where a2.PK1 = a.PK1 and a2.PK2 <= a.PK2) from TableA a) at
join bt
on at.PK1 = bt.FK1
and at.seq = bt.seq

nr
SQLTeam MVY

12543 Posts

Posted - 2007-08-12 : 14:22:40

update TableB
set FK2 = at.PK2
from
TableB b
join
(select PK, FK1, FK2, seq = (select count(*) from TableB b2 where b2.FK1 = b.FK1 and b2.FK2 <= b.FK2) from TableB b) bt
on b.PK = bt.PK
join
(select PK1, PK2, seq = (select count(*) from TableA a2 where a2.PK1 = a.PK1 and a2.PK2 <= a.PK2) from TableA a) at
on at.PK1 = bt.FK1
and at.seq = bt.seq

==========================================
Cursors are useful if you don't know sql.
DTS can be used in a similar way.
Beer is not cold and it isn't fizzy.

raffiq_eddy
Starting Member

12 Posts

Posted - 2007-08-13 : 01:25:13

It works!!

Thank you very much nr!

Regards

quote:
Originally posted by nr

update TableB
set FK2 = at.PK2
from
TableB b
join
(select PK, FK1, FK2, seq = (select count(*) from TableB b2 where b2.FK1 = b.FK1 and b2.FK2 <= b.FK2) from TableB b) bt
on b.PK = bt.PK
join
(select PK1, PK2, seq = (select count(*) from TableA a2 where a2.PK1 = a.PK1 and a2.PK2 <= a.PK2) from TableA a) at
on at.PK1 = bt.FK1
and at.seq = bt.seq

==========================================
Cursors are useful if you don't know sql.
DTS can be used in a similar way.
Beer is not cold and it isn't fizzy.

Hommer
Aged Yak Warrior

808 Posts

Posted - 2007-08-13 : 11:19:55

I found out this will also do the trick. I am not sure I follow the
logic of the 2nd join, but the way nr used the seq part is cool.

update TableB
set FK2 = bt.seq
from
TableB b
join
(select PK, FK1, FK2, seq = (select count(*) from TableB b2 where b2.FK1 = b.FK1 and b2.FK2 <= b.FK2) from TableB b) bt
on b.PK = bt.PK

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