Update row SQL in same table with data from other row

Question

I'm stuck with making a SQL query to update different rows, all in the same table. But 1 row has to get data from another row which has the same reference ID ( bst__ref ).

CURRENT TABLE bstlyn__

A	B	C	D	E	F	G
157035	1/01/1980	2/04/2021	117210	N	0	N
157035	1/01/1980	25/03/2021	128078	N	0	N
157035	1/01/1980	25/03/2021	128078	N	0	N
157036	1/01/1980	12/04/2021	117022	N	0	N
157036	1/01/1980	12/04/2021	117034	N	0	N
157036	1/01/1980	9/04/2021	128078	N	0	N

CURRENT SQL QUERY

UPDATE bstlyn__ SET G = 'Y', F = 'N', B = C WHERE E = 'N' AND F = '0'

This causes to change all vrz__dat lines to the same value as in vrzv_dat . But as you can see within the same bst__ref , the vrzv_dat of all afg__ref 's with value 128078 have a different vrzv_dat . This should be the same date/ vrz__dat like the (first) row from that bst__ref which hasn't got afg__ref 128078.

So, after running the query above I get:

bst__ref (A)	vrz__dat (B)	vrzv_dat (C)	afg__ref (D)	fiat____ (E)	fac__tst (F)	vrz__tst (G)
157035	2/04/2021	2/04/2021	117210	N	N	Y
157035	25/03/2021	25/03/2021	128078	N	N	Y
157035	25/03/2021	25/03/2021	128078	N	N	Y
157036	12/04/2021	12/04/2021	117022	N	N	Y
157036	12/04/2021	12/04/2021	117034	N	N	Y
157036	9/04/2021	9/04/2021	128078	N	N	Y

But it should be:

bst__ref	vrz__dat	vrzv_dat	afg__ref	fiat____	fac__tst	vrz__tst
157035	2/04/2021	2/04/2021	117210	N	N	Y
157035	2/04/2021	25/03/2021	128078	N	N	Y
157035	2/04/2021	25/03/2021	128078	N	N	Y
157036	12/04/2021	12/04/2021	117022	N	N	Y
157036	12/04/2021	12/04/2021	117034	N	N	Y
157036	12/04/2021	9/04/2021	128078	N	N	Y

How on Earth can I do this with only using SQL? Thanks!

Answer 1

You can use this table twice, you just need to alias the table in the subqueries. Then perform retrieval only of the first for each same A code

try this code:

UPDATE bstlyn__ t, (SELECT DISTINCT A,B,C,D,E,F,G
                    FROM bstlyn__ ) t1
SET t.B = t1.C, G = 'Y', F = 'N'
WHERE t.A= t1.A

Answer 2

You need to correlate back to the same table. There are various ways of accomplishing this, you appear to want to do this specifcally on a single value, so if I have understood correctly you can try this

update b set 
vrz__tst = 'Y',
fac__tst = 'N',
vrz__dat = 
    case when afg_ref=128078 then 
        (select Min(vrzv_dat) from bstlyn__ b2 where b2.bst_ref=b.bst_ref)
    else vrzv_dat end
from  bstlyn__ b
where fiat____ = 'N' and fac__tst = '0'