Alter a column default not taking effect after using the statement

Question

I am trying to alter a column's default value using

alter table table_Name alter MODIFY col_Name tinyint(1) NOT NULL DEFAULT 0;

After executing the above command, I see 25 rows affected. But when I run

select * from table_Name; I still see old value.

Moreover when I insert new value, I still see the default getting set as 1.Why is that?

Answer 1

When you set a default (as mentioned in the comments) old rows do NOT get affected.

Your original rows will stay as they are. To change them you need to do an UPDATE query

UPDATE TABLE table_name SET col_name=1 WHERE <condition>

Now as to why your new rows aren't updating. Your syntax is wrong. This is the correct syntax

alter table table_Name MODIFY col_Name tinyint(1) NOT NULL DEFAULT 0;

There is no second alter in after the table_name