Postgres 14

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create table tab1 (id int, v1 text, v2 text, v3 int);
create table tab2 (id int, v1 text, v2 text, v3 int);

insert into tab1
VALUES(1, 'A1', 'B1', 1),
(2, 'A2', 'B2', 0),
(3, 'A3', 'B3',1 ),
(4, 'A4', 'B4',1 ),
(5, 'A5', 'B5',0 ),
(6, 'A6', 'B6',1 );

insert into tab2 
VALUES(1, 'A1', 'B1', 0),
(2, 'A2', 'B2', 1),
(3, 'A3', 'B3', 1),
(6, 'A6', 'B6', 0);
6 rows affected

4 rows affected

UPDATE tab1 t1
SET v1 = concat(t1.v1,t2.v1)
FROM tab2 t2 
WHERE t1.id =t2.id AND
      t2.v3 > 0;
2 rows affected

SELECT * FROM tab1 ORDER BY id;


id
v1
v2
v3


1
A1
B1
1

2
A2A2
B2
0

3
A3A3
B3
1

4
A4
B4
1

5
A5
B5
0

6
A6
B6
1