Pre defined column with zero before image column [duplicate]

It seems INSERT and UPDATE do the same things to me.

Is there any occasions where I should use INSERT instead of UPDATE and vice versa?

In CRUD operations, the INSERT is the 'C' and the UPDATEis the 'U'. They are two of the four basic functions of persistent storage. The other two are SELECT and DELETE. Without at least these four operations, a typical database system cannot be considered complete.

Use INSERT to insert a new record.

Use UPDATE to update an existing record.

You cannot UPDATE a row that's not in a table.

You cannot INSERT a row that's already in a table.

Insert is for adding data to the table, update is for updating data that is already in the table.