'ALTER TABLE' 位必须先出现，然后每个部分必须用逗号分隔:

The 'ALTER TABLE' bit must come first, and then each part must be seperated by a comma:

ALTER TABLE gitags_items
DROP PRIMARY KEY,
ADD COLUMN id INT NOT NULL AUTO_INCREMENT FIRST,
ADD PRIMARY KEY (id,component,tag_id,item_id);

但我不确定您是否可以在同一个状态中删除和创建主键.

but I'm not sure if you can drop and create a primary key in the same staatement.