SQL Server 2017

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Create table tbl(
    id INT not null primary key,
    title varchar(100),
    newUrl varchar(100) unique,
)
-- CREATE UNIQUE INDEX newUrl on tbl(newUrl)
Insert INTO tbl(id, title, newUrl)  values (1,'test1', '40504')
Insert INTO tbl(id, title, newUrl)  values (2,'test2', '40505')
Insert INTO tbl(id, title, newUrl)  values (3,'test3', '40504')
Msg 2627 Level 14 State 1 Line 3
Violation of UNIQUE KEY constraint 'UQ__tbl__8C52427F31307BB9'. Cannot insert duplicate key in object 'dbo.tbl'. The duplicate key value is (40504).
Msg 3621 Level 0 State 0 Line 3
The statement has been terminated.

Select * from tbl


id
title
newUrl


1
test1
40504

2
test2
40505