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create table mytable(idx int, A int);
insert into mytable values(0, 1), (1, 1), (2, 3);
alter table mytable add column B varchar(10);
update mytable set B = A;
Records: 3 Duplicates: 0 Warnings: 0
Records: 0 Duplicates: 0 Warnings: 0
Rows matched: 3 Changed: 3 Warnings: 0
select * from mytable;
| idx | A | B |
|---|---|---|
| 0 | 1 | 1 |
| 1 | 1 | 1 |
| 2 | 3 | 3 |