Qu'est-ce que there is no unique constraint matching given keys for referenced table ?

"There is no unique constraint matching given keys for referenced table" is an error message that typically occurs in database systems, especially when using SQL. It means that a foreign key constraint cannot be satisfied because there is no matching unique constraint in the referenced table.

In a relational database, a foreign key is a field or a set of fields that refers to the primary key of another table, establishing a link or relationship between the two tables. This link is enforced through constraints to maintain data integrity.

When you attempt to create a foreign key relationship, the database engine checks if there is a matching unique constraint in the referenced table. The unique constraint can be the primary key of the referenced table or any other unique key.

If the error message "there is no unique constraint matching given keys for referenced table" is displayed, it means that the referenced table does not have a corresponding unique constraint that matches the foreign key(s) being used. This can happen due to various reasons, such as:

1. The referenced table does not have a primary key or any unique constraint defined.
2. The foreign key being used does not match any of the unique constraints in the referenced table.
3. The foreign key columns are of a different data type or length than the columns in the unique constraint.

To resolve this error, you need to ensure that there is a unique constraint in the referenced table that matches the foreign key(s) being used. This can involve altering the table structure to add a primary key or unique constraint on the appropriate column(s), or modifying the foreign key definition to match an existing unique constraint.

It's important to note that the specific steps to resolve this error may vary depending on the database management system you are using and the structure of your tables. Consulting the documentation or seeking assistance from an experienced database administrator can help in troubleshooting and resolving this error.