Postgres 13

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create table tablex (sellerid int , productid int, soldoutdate date);

create unique index ux_indx on tablex(sellerid, productid, coalesce(soldoutdate,'1990-01-01'));

insert into tablex values (1,1,now());

CREATE TABLE

CREATE INDEX

INSERT 0 1

select * from tablex;

sellerid
productid
soldoutdate

1
1
2023-12-08

SELECT 1

INSERT INTO tablex
VALUES (1, 1, NULL)
ON CONFLICT DO NOTHING;

INSERT 0 1

select * from tablex;

sellerid
productid
soldoutdate

1
1
2023-12-08

1
1
null

SELECT 2

INSERT INTO tablex
VALUES (1, 1, NULL)
ON CONFLICT DO NOTHING;

INSERT 0 0

select * from tablex;

sellerid
productid
soldoutdate

1
1
2023-12-08

1
1
null

SELECT 2

INSERT INTO tablex
VALUES (1, 1, NULL)
ON CONFLICT (sellerid, productid, coalesce(soldoutdate,'1990-01-01')) DO UPDATE set soldoutdate = '2020-01-10';

INSERT 0 1

select * from tablex;

sellerid
productid
soldoutdate

1
1
2023-12-08

1
1
2020-01-10

SELECT 2