What do you mean 'clustered' index?

[anonieko]

A lot of detailed discussion explains the difference between clustered
and non-clustered indexes. But very few 'clarifies' why the term used
is 'clustered'. Well, once and for all, this is my take.

*** The 'CLUSTERED' adjective refers to the INDEX being clustered (set
adjacent) to the DATA.

This means if you found the index, the data is already there beside it
(you don't have to look anywhere else). From this note, everything
hopefully becomes clearer to you. (You can now read further in the tech
book :-).
So, the next time you are asked to explain what is a clustered (or
non-clustered ) index think of the above.

[Tony Rogerson]

Slight variation:

Data is clustered WITH the index, basically the index leaf level is the
actual data whereas on non-clustered indexes the leaf level of the index is
a copy of the data (just the key columns) and a bookmark (if table is a heap
then a pointer otherwise its a copy of the clustering key).

Tony.

--
Tony Rogerson
SQL Server MVP
http://sqlblogcasts.com/blogs/tonyrogerson - technical commentary from a SQL
Server Consultant
http://sqlserverfaq.com - free video tutorials
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>A lot of detailed discussion explains the difference between clustered
and non-clustered indexes. But very few 'clarifies' why the term used
is 'clustered'. Well, once and for all, this is my take.

*** The 'CLUSTERED' adjective refers to the INDEX being clustered (set
adjacent) to the DATA.

This means if you found the index, the data is already there beside it
(you don't have to look anywhere else). From this note, everything
hopefully becomes clearer to you. (You can now read further in the tech
book :-).
So, the next time you are asked to explain what is a clustered (or
non-clustered ) index think of the above.