One of my colleagues showed me this gem in Oracle and I thought of documenting it here so that it will be useful for everyone and also I can find it next time I need it by just searching my blog instead of Google. 🙂 Using this query you can find out the start time of the Oracle database server.
SELECT * FROM V$INSTANCE
In addition to the start time the query also returns other useful information like instance name, version, hostname etc. The hostname is particularly useful when TNSNAMES.ORA is playing tricks with you.