Database Reference
In-Depth Information
oracle server, we can say that there are three sessions with oracle
server. If one person logs off then the number of sessions drops
to two. The connected users use SQL commands (like SELECT,
UPDATE, INSERT etc. which we will learn in detail in chapter
ahead) to communicate with Oracle server.
SQL commands are very simple and very easy to master, as it is
comprised of all full-length English words with no or very little
abbreviations. For example lets have a look on following SQL
command
SELECT name, phone
FROM address_book;
Once Oracle Instance will receive this command, it will retrieve
all the “name” and “phone” information from the address_book
table and send it to the user. If there are 1000 records or rows in
that table; all of them gets sent to user computer.
If the user wants to see all those people having name beginning
with letter “A”. To make this happen we have to use the
“WHERE” clause of SELECT Statement.
SELECT name, phone
FROM address_book
WHERE name LIKE “A*”;
Thus you have seen how simple the SQL language is. Let me put
it this way anyone who can read and understand English, can
learn SQL with very small efforts.
Understanding of Instance, Database and Session are considered
as the foundation. You should not forget the concept and
meaning of these three terms as we are going to build the Oracle
Architecture concept over it and we will be using these terms in
the upcoming discussion. So let me define these three terms one
by one.
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