How can I merge two MySQL tables?

How can I merge two MySQL tables that have the same structure?

The primary keys of the two tables will clash, so I have take that into account.

You can also try:

INSERT IGNORE
  INTO table_1 
SELECT *
  FROM table_2
     ;

which allows those rows in table_1 to supersede those in table_2 that have a matching primary key, while still inserting rows with new primary keys.

Alternatively,

REPLACE
   INTO table_1
 SELECT *
   FROM table_2
      ;

will update those rows already in table_1 with the corresponding row from table_2, while inserting rows with new primary keys.

It depends on the semantic of the primary key. If it's just autoincrement, then use something like:

insert into table1 (all columns except pk)
select all_columns_except_pk 
from table2;

If PK means something, you need to find a way to determine which record should have priority. You could create a select query to find duplicates first (see https://stackoverflow.com/questions/725556/how-can-i-merge-two-mysql-tables/725571#725571">answer by cpitis). Then eliminate the ones you don't want to keep and use the above insert to add records that remain.

INSERT
INTO    first_table f
SELECT  *
FROM    second_table s
ON DUPLICATE KEY
UPDATE
        s.column1 = DO_WHAT_EVER_MUST_BE_DONE_ON_KEY_CLASH(f.column1)

If you need to do it manually, one time:

First, merge in a temporary table, with something like:

create table MERGED as select * from table 1 UNION select * from table 2

Then, identify the primary key constraints with something like

SELECT COUNT(*), PK from MERGED GROUP BY PK HAVING COUNT(*) > 1

Where PK is the primary key field...

Solve the duplicates.

Rename the table.

[edited - removed brackets in the UNION query, which was causing the error in the comment below]

Not as complicated as it sounds.... Just leave the duplicate primary key out of your query.... this works for me !

INSERT INTO
  Content(
    `status`,
    content_category,
    content_type,
    content_id,
    user_id,
    title,
    description,
    content_file,
    content_url,
    tags,
    create_date,
    edit_date,
    runs
  )
SELECT `status`,
  content_category,
  content_type,
  content_id,
  user_id,
  title,
  description,
  content_file,
  content_url,
  tags,
  create_date,
  edit_date,
  runs
FROM
  Content_Images

You could write a script to update the FK's for you.. check out this blog: http://multunus.com/2011/03/how-to-easily-merge-two-identical-mysql-databases/

They have a clever script to use the information_schema tables to get the "id" columns:

SET @db:='id_new'; 

select @max_id:=max(AUTO_INCREMENT) from information_schema.tables;

select concat('update ',table_name,' set ', column_name,' = ',column_name,'+',@max_id,' ; ') from information_schema.columns where table_schema=@db and column_name like '%id' into outfile 'update_ids.sql';
 
use id_new
source update_ids.sql;