Renaming foreign-key columns in MySQL

Question

We\'re trying to rename a column in MySQL (5.1.31, InnoDB) that is a foreign key to another table.

At first, we tried to use Django-South, but came up against a know

Answer 1

Expanding on @Dewey's answer, here's a little script to rename FKs generated by Hibernate in a useful manner ("FK__" + table name + "__" + referenced table name).

SELECT CONCAT(
  "alter table ", TABLE_NAME, " drop foreign key ", CONSTRAINT_NAME,";\n",
  "alter table ", TABLE_NAME, " drop key ", CONSTRAINT_NAME, ";\n",
  "alter table ", TABLE_NAME, " add key FK__", table_name, "__",
      referenced_table_name, " (", column_name, ");\n",
  "alter table ", TABLE_NAME, " add constraint FK__", table_name, "__",
      referenced_table_name , " foreign key (", column_name, ") ",
      "references ", referenced_table_name,
      "(", referenced_column_name, ");"
  ) AS runMe 
FROM
  information_schema.key_column_usage
WHERE 
  TABLE_SCHEMA='myschemaname' 
  AND 
  constraint_name like 'FK_%';

A bit of output:

alter table visitor_browsers drop foreign key FK_4ygermmic4fujggq1kp96dx47;
alter table visitor_browsers drop key FK_4ygermmic4fujggq1kp96dx47;
alter table visitor_browsers add key FK__visitor_browsers__websites (website);
alter table visitor_browsers add constraint FK__visitor_browsers__websites foreign key (website) references websites(id);

Answer 2

This task becomes simpler if you use GUI tools. I tried to rename ID column using IntelliJ IDEA Database tool and it worked like a charm! I don't have to bother about foreign keys when renaming a table or column.

See more details in IntelliJ IDEA Help | Renaming items.

Answer 3

AFAIK, dropping the constraint, then rename, then add the constraint back is the only way. Backup first!

Answer 4

The following query will build the correct syntax automatically. Just execute each line returned and all your FKEYs will be gone.

I leave the reverse (adding them back) as an exercise for you.

SELECT CONCAT("alter table ", TABLE_NAME," drop foreign key `", CONSTRAINT_NAME,"`; ") AS runMe
FROM information_schema.key_column_usage 
WHERE TABLE_SCHEMA='MY_SCHEMA_NAME';

Answer 5

In case anyone is looking for the syntax it goes something like this:

alter table customer_account drop foreign key `FK3FEDF2CC1CD51BAF`; 

alter table customer_account  add constraint `FK3FEDF2CCD115CB1A` foreign key (campaign_id) REFERENCES campaign(id);

Answer 6

here is the SQL syntax for regular keys

ALTER TABLE `thetable`
  DROP KEY `oldkey`, 
  ADD KEY `newkey` (`tablefield`);