Mysql cannot add foreign key constraint

MySql and creating Foreign keys. Cannot add foreign key constraint. The table or index in the constraint references misuses quotes.

How to diagnose: Inspect each FOREIGN KEY declaration and make sure you either have no quotes around object qualifiers or that you have quotes around the table and a SEPARATE pair of quotes around the column name. There’s actually a multitude of reasons this can happen. In some RDBMS, for example SQL Server, you can reference a column with a unique index (not key ) (see can we have a foreign key which is not a primary key in any other table?), but this is non-standard behavior. Only MySQL storage engine InnoDB supports foreign key , make sure you are using InnoDB storage engine. You can use the following command to determine which storage engine your server supports.

Is there any existing data that the table contains? If so, try to clear out all the data in the table you want to add a foreign key. Then run the code ( add a foreign key ) again. I encountered this problem so many times. This clearing out the all data in the table works when you want to add foreign key on a existing table.

You must first insert the row to your Ordre table. Documentation Downloads MySQL. Secondary indexes are not supported on virtual columns that have a base column that is referenced in a foreign key constraint : the foreign key constraint in the example should not use the faulty secondary index. Seems that foreign key options cannot be left undefined! CONSTRAINT `fk_Rent_Status_Code` FOREIGN KEY (`status_code`) REFERENCES `test`.

Lose the unique declarations. Summary: in this tutorial, you will learn about MySQL foreign key and how to create, drop, and disable a foreign key constraint. Introduction to MySQL foreign key.

A foreign key is a column or group of columns in a table that links to a column or group of columns in another table. MySQL supports foreign keys , which let you cross-reference related data across tables, and foreign key constraints , which help keep this spread-out data consistent. A FOREIGN KEY is a key used to link two tables together. Sorry, only registered users may post in this forum. Content reproduced on this site is the property of the respective copyright holders.

Greetings, I am a student learning SQL so I apologize in advance for the naive questions. You need to have already declared the table that the foreign key references, before you can define a foreign key that references it. Once you declare the second table, you can then declare the first table. However, even if foreign _ key _checks = MySQL does not permit the creation of a foreign key constraint where a column references a nonmatching column type. Also, if a table has foreign key constraints, ALTER TABLE cannot be used to alter the table to use another storage engine.

Java Project Tutorial - Make Login and Register Form Step by Step Using NetBeans And MySQL Database - Duration: 3:43:32. Browse other questions tagged mysql foreign - key. In this video, we propose a solution for the well-known error that may occur after.

Like MySQL in general, in an SQL statement that inserts, deletes, or updates many rows, InnoDB checks UNIQUE and FOREIGN KEY constraints row-by-row. When performing foreign key checks, InnoDB sets shared row-level locks on child or parent records it has to look at. Pessoal ja pesquisei vários outros tópicos sobre este erro e nenhum resolveu o meu problema por isto estou postando aqui para vocês.