MS SQL Server INSERT值如果为NULL

Question

Good day

I have Table1:

COLUMN1    COLUMN2   Column3
----------------------------
1             A        K
2             NULL     K
3             NULL     D
...           ...      ...

I need

COLUMN1    COLUMN2   Column3
----------------------------
1             A        A
2             K        K
3             D        D
...           ...      ...

I am stuck with my code and I cannot understand why server tries to insert into COLUMN3 ?

Thanks for any opinions

INSERT INTO Table1 (COLUMN2)
    SELECT CLoumn3
    FROM Table1
    WHERE Column2 IS NULL; 

Resulting error:

Msg 515, Level 16, State 2, Line 1
Cannot insert the value NULL into column 'Column3', table 'TABLE1'; column does not allow nulls. INSERT fails.

This is only example original table have more columns.

Answer 1

I think you want an update :

update table1
    set column2 = column3
    where column2 is null;

insert inserts new rows into a table. update changes the values in existing rows.