mysql combined unique keys

Question

Is there way in MySQL to have two unique keys and connect them somehow?

for example if i have the following table and 'title'and 'store' are a unique keys

id | category | title       | price | store
1  | outdoors | fishing rod | 59.99 | wal-mart
2  | auto     | Penzoil Oil | 9.99  | target

and i try to insert the following record. This new record would be ignored because the title is "fishing rod" AND the store is 'wal-mart' and there is an existing record with that title and store

   | outdoors | fishing rod | 30.99 | wal-mart

but if i attempted to insert the following record it would be accepted because there isn't a record that exists with the title of "fishing rod" and store of "target"

   | outdoors | fishing rod | 30.99 | target

is this possible with just MySQL?

Answer 1

You can define an index on multiple columns, e.g.:

CREATE UNIQUE INDEX arbitrary_index_name ON table_name (title, store);

Answer 2

Yes. Instead of two separate unique constraints you should create a single unique constraint on both columns.

The CREATE INDEX syntax is:

CREATE [UNIQUE|FULLTEXT|SPATIAL] INDEX index_name
    [index_type]
    ON tbl_name (index_col_name,...)
    [algorithm_option | lock_option] ...

For your example it would look something like this:

CREATE UNIQUE INDEX index_name ON tbl_name (title,store);

You will also have to drop the two incorrect unique indexes that you created.

See the documentation for more details on how to create indexes.

Answer 3

You need a multi-column unique key.

Answer 4

ALTER TABLE table_name ADD UNIQUE INDEX( title, store);

Answer 5

Yes you can!

ALTER TABLE table_name DROP PRIMARY KEY;
ALTER TABLE table_name ADD PRIMARY KEY(title, store);