Does using msql_select_db excessively burn resources?

[seek]

I plan to have my sites using several databases, but there is a common database they must all use. Obviously I'll have to use "mysql_select_db" each time I change the database I wish to use. Does this simply select the database and hold it as a variable until a query is made, or does it load it in a way that would potentially slow things down?

[mattr]

It actually executes "USE database", or that is what PHP does in other DBMS libs. Take a look in the source, that is why it is provided to you!

In any rate, if you are already connected in a database no need to change contexts; simply use the database.tablename convention in your query:

SELECT *
  FROM other_database.table