Setting up foreign keys in phpMyAdmin?

I'm setting up a database using phpMyAdmin. I have two tables (foo and bar), indexed on their primary keys. I am trying to create a relational table (foo_bar) between them, using their primary keys as foreign keys.

I created these tables as MyISAM, but have since changed all three to InnoDB, because I read that MyISAM doesn't support foreign keys. All id fields are INT(11).

When I choose the foo_bar table, click the "relation view" link, and try to set the FK columns to be database.foo.id and database.bar.id, it says "No index defined!" beside each column.

What am I missing?

Clarification/Update

For the sake of simplicity, I want to keep using phpMyAdmin. I am currently using XAMPP, which is easy enough to let me focus on the PHP/CSS/Javascript, and it comes with phpMyAdmin.

Also, although I haven't been able to set up explicit foreign keys yet, I do have a relational table and can perform joins like this:

SELECT * 
FROM foo 
INNER JOIN foo_bar 
ON foo.id = foo_bar.foo_id 
INNER JOIN bar
ON foo_bar.bar_id = bar.id;

It just makes me uncomfortable not to have the FKs explicitly defined in the database.

 Answers

If you want to use phpMyAdmin to set up relations, you have to do 2 things. First of all, you have to define an index on the foreign key column in the referring table (so foo_bar.foo_id, in your case). Then, go to relation view (in the referring table) and select the referred column (so in your case foo.id) and the on update and on delete actions.

I think foreign keys are useful if you have multiple tables linked to one another, in particular, your delete scripts will become very short if you set the referencing options correctly.

EDIT: Make sure both of the tables have the InnoDB engine selected.

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This is a summary of a Wikipedia article. It specifies the different types of relationships you can stipulate in PHPmyadmin. I am putting it here because it is relevant to @Nathan's comment on setting the foreign keys options for "on update/delete" but is too large for a comment - hope it helps.

CASCADE

Whenever rows in the master (referenced) table are deleted (resp. updated), the respective rows of the child (referencing) table with a matching foreign key column will get deleted (resp. updated) as well. This is called a cascade delete (resp. update[2]).

RESTRICT

A value cannot be updated or deleted when a row exists in a foreign key table that references the value in the referenced table. Similarly, a row cannot be deleted as long as there is a reference to it from a foreign key table.

NO ACTION

NO ACTION and RESTRICT are very much alike. The main difference between NO ACTION and RESTRICT is that with NO ACTION the referential integrity check is done after trying to alter the table. RESTRICT does the check before trying to execute the UPDATE or DELETE statement. Both referential actions act the same if the referential integrity check fails: the UPDATE or DELETE statement will result in an error.

SET NULL

The foreign key values in the referencing row are set to NULL when the referenced row is updated or deleted. This is only possible if the respective columns in the referencing table are nullable. Due to the semantics of NULL, a referencing row with NULLs in the foreign key columns does not require a referenced row.

SET DEFAULT

Similar to SET NULL, the foreign key values in the referencing row are set to the column default when the referenced row is updated or deleted.

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For those new to database .... and need to ALTER an existing table. A lot things seem to be pretty straightforward, but there is always something ... between A and B.

Before anything else, take a look at this.

1. Make sure you have P_ID (parent ID on both parent and child table).
2. Of course it will be already filled in the parent. Not necessarily in the child in a true and final way. So for instance P_ID #3 (maybe many times in the child table will be pointing to original P_ID at parent table).
3. Go to SQL tab (I am using phpMyAdmin, should be similar in other ones) and do this command:
   ALTER TABLE child_table_name
   ADD FOREIGN KEY (P_ID)
   REFERENCES parent_table_name (P_ID)
4. Click on child table, than structure, finally on relational view. Finish your DB planning there. There was a nice answer before this one about cascade, restrict, etc. Of course it could be done by commands...

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InnoDB allows you to add a new foreign key constraint to a table by using ALTER TABLE:

ALTER TABLE tbl_name
    ADD [CONSTRAINT [symbol]] FOREIGN KEY
    [index_name] (index_col_name, ...)
    REFERENCES tbl_name (index_col_name,...)
    [ON DELETE reference_option]
    [ON UPDATE reference_option]

On the other hand, if MyISAM has advantages over InnoDB in your context, why would you want to create foreign key constraints at all. You can handle this on the model level of your application. Just make sure the columns which you want to use as foreign keys are indexed!

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Step 1: You have to add the line: default-storage-engine = InnoDB under the [mysqld] section of your mysql config file (my.cnf or my.ini depending on your OS) and restart the mysqld service.

Step 2: Now when you create the table you will see the type of table is: InnoDB

Step 3: Create both Parent and Child table. Now open the Child table and select the column U like to have the Foreign Key: Select the Index Key from Action Label as shown below.

Step 4: Now open the Relation View in the same child table from bottom near the Print View as shown below.

Step 5: Select the column U like to have the Foreign key as Select the Parent column from the drop down. dbName.TableName.ColumnName

Select appropriate Values for ON DELETE and ON UPDATE