Changes

==Alternative keys==

==Alternative keys==

Sometimes, we need another unique keys than primary key. We can add in this case an alternate unique key. When we need this, we can create an alternate unique key. Such an index is called by a name that start by prefix <tt>uk_</tt> followed by an underscore, then the the table name (this is required to avoid duplicate names of unique keys that may create problems for some DBMS like Postgresql) and then another string to define the key (this is to allow to have several unique keys on same table).

Sometimes, we need other unique keys than primary key. When we need this, we can create an alternate unique key. Such a key should have a name that starts with <tt>uk_</tt>, then the table name (this is required to avoid duplicate names of unique keys that may create problems for some DBMS like Postgresql) and then another string to define the key (this is to allow having several unique keys on the same table).

Example:

Example: