queries
to extract information from the RDB
- present it with a query
- examples
who won the java-jump event?
what company is sponsoring ben?
which company sponsored the winner of the java-jump event?
kinds of query
- some queries can be answered by examining only one table
who won the java-jump event? –> look at EVENTS table
what company is sponsoring ben? –> look at ATHLETES table
- some need more than one table
which company sponsored the winner of the java-jump event?
–> look up winner in EVENTS and then find sponsor in ATHLETES
query processing
- queries are declarative: they say what you want, not how to get it
- database system translates query into operation on internal data structures
- may optimize the query before applying, so that it goes faster