備忘：Alter Table中: ALTER vs CHANGE vs MODIFY COLUMN 區別

三者區別在於：

ALTER COLUMN 改默認值的。

Used to set or remove the default value for a column. Example:

ALTER TABLE MyTable ALTER COLUMN foo SET DEFAULT 'bar';
ALTER TABLE MyTable ALTER COLUMN foo DROP DEFAULT;

CHANGE COLUMN 包含改列名的。

Used to rename a column, change its datatype, or move it within the schema. Example:

ALTER TABLE MyTable CHANGE COLUMN foo bar VARCHAR(32) NOT NULL FIRST;
ALTER TABLE MyTable CHANGE COLUMN foo bar VARCHAR(32) NOT NULL AFTER baz;

MODIFY COLUMN 不必改列名的其它修改。

Used to do everything CHANGE COLUMN can, but without renaming the column. Example:

ALTER TABLE MyTable MODIFY COLUMN foo VARCHAR(32) NOT NULL AFTER baz;