- Original Message -
From: Aji Andri [EMAIL PROTECTED]
To: mysql@lists.mysql.com
Sent: Saturday, April 02, 2005 2:13 AM
Subject: Newbie :create table multi, index
hi seniors,
I assume that English is not your first language. Seniors means old
people and some people would be offended by being called old if they are
not old ;-)
I'm trying to create a table, here my table
properties,
create table user (
UserID int primary,
Password varchar (20),
User_stats int multi
);
i'm still confuse in User_stats properti's that is
multi,
what really use 'multi' is ?
and what the conection between primary key and index
I don't know what you are trying to do with the word 'multi'. If you look at
the article in the manual that describes CREATE TABLE -
http://dev.mysql.com/doc/mysql/en/create-table.html - the word 'multi' is
not one that belongs in a CREATE TABLE statement. I assume that 'user_stats'
is the name that you want to give to your third column and you want the
datatype to be 'int'. That's fine, but I don't see what you want the word
'multi' to do in that statement.
The primary key clause in your statement tells MySQL that the columns named
in the clause uniquely identify each row in the table. For example, if you
say
primary key(UserID)
you are saying that each row of the table has a different, non-null, value
in UserID. In other words, each row in the table can be uniquely identified
by the value of UserID; you will never get two or more rows that have the
same UserID. This is very important because most updates will be made based
on the primary key value and you will want to be sure that only the desired
row gets updated.
An index is a shortcut that helps the database find rows more quickly.
However, if you have no indexes, the database will still be able to find the
rows that satisfy your query. An index in a database is very similar to an
index in a reference book: if you have an index in a book, you can look up
the information you want in the index and you will see that the information
can be found on page 27; then, you can go to page 27 and find the exact
information. If you don't have an index, you can still find the information
but you'll have to read every page of the book to find it, which will
usually take much longer.
Database designers usually created indexes on the primary keys of tables. In
fact, some databases *automatically* build primary key indexes.
However, indexes don't have to be unique. You can create indexes on
non-unique columns of a table if you like. For instance, if you had a column
listing the name of the city in which your customers live, you can create an
index on that column. Then, if you want to find all the rows where the city
is Tokyo, the index will help the database find all the Tokyo customers
faster.
Non-unique indexes normally have to be built manually via CREATE INDEX
statements.
Rhino
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