Searching a database requires the construction of an SQL string that specifies the database, the table and the field that will hold the queried parameter.
In order to do this on an entire DB, you'd need to construct either a very long piece of SQL if you know all the field names or depending on the DB return the column names from the schema using something like this in mySQL:
Code:
select table_name, column_name, data_type from information_schema.columns where TABLE_SCHEMA = "name of database"
This could then be used to create a loop that would substitute the column names from the returned values above and run the query against each.
I'd be inclined to post / continue this topic in the advanced section (which is for databases) as I don't think there is some quick and easy solution to your question. You might also post a fuller description as to your aim as it's not that often an entire DB would need to be queried - else they'd have built in commands for it.
Mack