mysql – Error 1022 – Can’t write; duplicate key in table

The Question :

228 people think this question is useful

I’m getting a 1022 error regarding duplicate keys on create table command. Having looked at the query, I can’t understand where the duplication is taking place. Can anyone else see it?

SQL query:

-- -----------------------------------------------------
-- Table `apptwo`.`usercircle`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS  `apptwo`.`usercircle` (

 `idUserCircle` MEDIUMINT NOT NULL ,
 `circleId` MEDIUMINT NULL ,
 `authUser` BINARY NULL ,
 `authOwner` BINARY NULL ,
 `startDate` DATETIME NULL ,
 `endDate` DATETIME NULL ,
PRIMARY KEY (  `idUserCircle` ) ,
INDEX  `iduser_idx` (  `userId` ASC ) ,
INDEX  `idcategory_idx` (  `circleId` ASC ) ,
CONSTRAINT  `iduser` FOREIGN KEY (  `userId` ) REFERENCES  `apptwo`.`user` (
CONSTRAINT  `idcategory` FOREIGN KEY (  `circleId` ) REFERENCES  `apptwo`.`circle` (

MySQL said: Documentation

#1022 - Can't write; duplicate key in table 'usercircle' 

The Question Comments :
  • If I remember correctly, the primary key is always also a UNIQUE INDEX, so you would have to drop the unique index statement?
  • ON DELETE NO ACTION would just drop the entire use of the foreign key. Unless you have very specific reasons to do that.
  • @AmazingDreams Why? It still enforces referential integrity. Only you have to delete the children yourself. This is safer than a cascaded delete where you could accidentally delete lots of data by deleting one incorrect keyword.
  • Why use an alias when using the ‘aliased’ makes the purpose clear immediately?
  • @AmazingDreams Thanks for the tip. I like the debate around it as well – it helps me to learn about the pros and cons.

The Answer 1

559 people think this answer is useful

The most likely you already have a constraint with the name iduser or idcategory in your database. Just rename the constraints if so.

Constraints must be unique for the entire database, not just for the specific table you are creating/altering.

To find out where the constraints are currently in use you can use the following query:

FROM `information_schema`.`KEY_COLUMN_USAGE`
WHERE `CONSTRAINT_NAME` IN ('iduser', 'idcategory');

The Answer 2

31 people think this answer is useful

Change the Foreign key name in MySQL. You can not have the same foreign key names in the database tables.

Check all your tables and all your foreign keys and avoid having two foreign keys with the same exact name.

The Answer 3

15 people think this answer is useful

From the two linksResolved Successfully and Naming Convention, I easily solved this same problem which I faced. i.e., for the foreign key name, give as fk_colName_TableName. This naming convention is non-ambiguous and also makes every ForeignKey in your DB Model unique and you will never get this error.

Error 1022: Can’t write; duplicate key in table

The Answer 4

6 people think this answer is useful

As others have mentioned, it’s possible that the name for your constraint is already in use by another table in your DB. They must be unique across the database.

A good convention for naming foreign key constraints is:


To investigate whether there’s a possible clash, you can list all constraints used by your database with this query:

SELECT * FROM information_schema.table_constraints WHERE constraint_schema = 'YOUR_DB';

When I ran this query, I discovered I had previously made a temporary copy of a table and this copy was already using the constraint name I was attempting to use.

The Answer 5

4 people think this answer is useful

I just spent the last 4 hours with the same issue. What I did was to simply make sure the constraints had unique names.

You can rename the constraints. I appended a number to mine so I could easily trace the number of occurrences.


If a constraint in a table is named boy with a foreign key X The next constraint with the foreign key X can be called boy1

I’m sure you’d figure out better names than I did. 🙂

The Answer 6

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This can also arise in connection with a bug in certain versions of Percona Toolkit’s online-schema-change tool. To mutate a large table, pt-osc first creates a duplicate table and copies all the records into it. Under some circumstances, some versions of pt-osc 2.2.x will try to give the constraints on the new table the same names as the constraints on the old table.

A fix was released in 2.3.0.

See for more details.

The Answer 7

1 people think this answer is useful

I also encountered that problem.Check if database name already exist in Mysql,and rename the old one.

The Answer 8

1 people think this answer is useful

I had this problem when creating a new table. It turns out the Foreign Key name I gave was already in use. Renaming the key fixed it.

The Answer 9

0 people think this answer is useful

You are probably trying to create a foreign key in some table which exists with the same name in previously existing tables. Use the following format to name your foreign key



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