# Background <!-- A clear and concise description of what the problem is --> Online ddl will copy the whole table data when renaming a column. ``` set @@ddl_strategy='online'; alter table mysql.t1 rename column username to user_name; ``` # Proposal <!-- A clear and concise description of what you want to happen. --> Identify these cases.
Background
Online ddl will copy the whole table data when renaming a column.
Proposal
Identify these cases.