mysql中有三种修改列的语句
ALTER [COLUMN] col_name {SET DEFAULT literal | DROP DEFAULT}
CHANGE [COLUMN] old_col_name new_col_name column_definition
MODIFY [COLUMN] col_name column_definition
他们的区别
CHANGE:
Can rename a column and change its definition, or both.
Has more capability than MODIFY, but at the expense of convenience for some operations. CHANGE requires naming the column twice if not renaming it.
With FIRST or AFTER, can reorder columns.
MODIFY:
Can change a column definition but not its name.
More convenient than CHANGE to change a column definition without renaming it.
With FIRST or AFTER, can reorder columns.
ALTER: Used only to change a column default value.
