MySQL alter table add column with primary key syntax error

Question

I'm trying to add a column to one of of my database tables, but there is a syntax error and I can't seem to find the problem...

My current database table looks like this:

component   +  tag_id  +  item_id
------------|----------|-----------
com_content |    23    |    2642
com_content |    26    |    3481
com_content |    35    |    1868
com_content |    85    |    5827
com_content |    89    |    7882

I want it to look like this, where 'id' is auto increment and all columns part of the primary key

 id  +  component   +  tag_id  +  item_id
-----|--------------|----------|-----------
  1  |  com_content |    23    |    2642
  2  |  com_content |    26    |    3481
  3  |  com_content |    35    |    1868
  4  |  com_content |    85    |    5827
  5  |  com_content |    89    |    7882

This is my query:

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

However I'm getting this error message:

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'PRIMARY KEY ALTER TABLE gitags_items ADD COLUMN id INT NOT NULL AUTO_INC' at line 1

Any help/pointers would be much appreciated

Answer 1

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);

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

Answer 2

这个工作正常，有逗号的问题，因为你要自己设置一个主键，所以不需要丢弃主键

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

Answer 3

首先，您必须在设置自动增量之前创建“id”列主键。

Answer 4

Try to add the following code to my.cnf

sql-mode="NO_ENGINE_SUBSTITUTION,ERROR_FOR_DIVISION_BY_ZERO"

then, restart MySQL

# service mysqld restart