'The duplicate key value is (<NULL>, <NULL>) but I don't have that result?

I'm getting the following error when I try to add 3 more columns data to my existing table

> Cannot insert duplicate key row in object 'dbo.table1' with unique
> index 'IX_OL_column1_column2'. The duplicate key value is (<NULL>,
> <NULL>).

Here is my code

INSERT INTO table1 (column3, column4, column5)
select t2.column3, t2.column4, t3.column5
from table1 t1
         left join [database1].dbo.table2 t2 on t1.column6 = cast(t2.column6 as nvarchar)
         left join [database2].dbo.table3 t3
                   on t1.column1 = t3.column1 and t1.column2 = t3.column2
where t1.column7 = 0

The thing is, when I run the select command alone while adding column1 and column2 to see the result, there is never a case where the both of them are NULL.

What could be the issue here?

sqlduplicates


Solution 1:[1]

The solution is: my syntax is wrong, it should be UPDATE table1 SET

Sources

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Source: Stack Overflow

Solution Source
Solution 1 Saja

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