SQL Server 2019

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create table GSDTS ( PNM int, ITM varchar(100), QTY int, CIU int, NOD int, DPR int);
insert into GSDTS values(1000,    'TEST 1000',   10,  10000,   01,  5);
insert into GSDTS values(1000,    'TEST 1001',   5,   20000,   02,  10);
insert into GSDTS values(1002,    'TEST 1000',   12,  10000,   01,  15);
insert into GSDTS values(1002,    'TEST 1001',   6,   20000,   02,  6);
4 rows affected


create table GSGTS (GDN varchar(50), PNM int, BLC int);
insert into GSGTS values('A.04.01.002.001',1000,    0);
insert into GSGTS values('A.04.01.002.001',1002,    0);
2 rows affected

select * from GSGTS


GDN
PNM
BLC


A.04.01.002.001
1000
0

A.04.01.002.001
1002
0


update GSGTS SET BLC=( select sum((qty*ciu)*(1-dpr/100.0)) from GSDTS t2 WHERE GSGTS.[PNM] = t2.[PNM] ) WHERE GDN = 'A.04.01.002.001';
2 rows affected

select * from GSGTS


GDN
PNM
BLC


A.04.01.002.001
1000
185000

A.04.01.002.001
1002
214800