MySQL insert into table with auto-increment while selecting from another table

Question

I have a table with an auto-increment primary key:

create table rt_table
(
  rtID int PRIMARY KEY AUTO_INCREMENT, 
  rt_user_id BIGINT,               /*user being retweeted*/
  rt_user_name varchar(70),        /*user name of rt_user_id*/
  source_user_id BIGINT,           /*user tweeting rt_user_id*/
  source_user_name varchar(70),    /*user name of source_user_id*/
  tweet_id BIGINT,                 /*fk to table tweets*/

  FOREIGN KEY (tweet_id) references tweets(tweet_id)
);

I wish to populate this table from parts of another table:

insert into rt_table 
select rt_user_id, (select user_name from users u where u.user_id = t.rt_user_id),
       source_user_id, (select user_name from users u where u.user_id = t.source_user_id),
       tweet_id
  from tweets t
 where rt_user_id != -1;

I get an error which says the number of columns do not match up, which is because of the primary key (which is an auto-incremented value and thus does not need to be set). How do I get around this?

score 31 · Accepted Answer · answered Jul 21 '13 at 15:23

You need to explicitly list the columns in the insert statement:

insert into rt_table (rt_user_id, rt_user_name, source_user_id, source_user_name, tweet_id)
select rt_user_id, (select user_name from users u where u.user_id = t.rt_user_id),
       source_user_id, (select user_name from users u where u.user_id = t.source_user_id),
       tweet_id
  from tweets t
 where rt_user_id != -1;

Also, I think it is better form to use explicit joins, rather than nested selects:

insert into rt_table (rt_user_id, rt_user_name, source_user_id, source_user_name, tweet_id)
    select t.rt_user_id, u.user_name, t.source_user_id, su.user_name, t.tweet_id
    from tweets t left outer join
         users u
         on t.rt_user_id = u.user_id left outer join
         users su
         on t.source_user_id = su.user_id
    where rt_user_id != -1;

This often (but not always) helps the optimizer find the best query plan.

score 30 · Answer 2 · edited Feb 19 '15 at 18:18

30

You simply set the primary key to NULL during the insert.

INSERT INTO rt_table 
SELECT 
  NULL,
  rt_user_id,
  (SELECT 
    user_name 
  FROM
    users u 
  WHERE u.user_id = t.rt_user_id),
  source_user_id,
  (SELECT 
    user_name 
  FROM
    users u 
  WHERE u.user_id = t.source_user_id),
  tweet_id 
FROM
  tweets t 
WHERE rt_user_id != - 1 ;

edited Feb 19 '15 at 18:18

konung

6,908
6
54
79

answered Apr 07 '14 at 16:15

Styphon

10,304
9
52
86

MySQL insert into table with auto-increment while selecting from another table

2 Answers2