How can I merge two MySQL tables? - sql

Question

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.

Answer 1

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.

Answer 2

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 answer by cpitis). Then eliminate the ones you don't want to keep and use the above insert to add records that remain.

Answer 3

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)

Answer 4

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]

Answer 5

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

Answer 6

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;