User Guide

SAP AG November 2002
Table Access (SELECT) using B* Tree (1)
SELECT FROM
address WHERE
city = 'Athens'
SELECT FROM
address WHERE
city = 'Athens'
Wa
Az Baf ... ... Bi
Waf
...
..
Zu
Aalen Amiens Anizy Athens Auber Avon
.. .. ..
Anizy s..
Anizy |France
Greece
Root Level
Index Level
Leaf Level
Athens < Ba ?
Yes ⇒
Follow leftmost address
Athens < Ba ?
Yes ⇒
Follow leftmost address
Athens < Au ?
Yes ⇒
Follow address ‘An’
Athens < Au ?
Yes ⇒
Follow address ‘An’
Au
Ba
Athen.
Athens |..
An
The address table is defined via the city primary key [Page
101] column. In the address table,
the system is to search for an entry with value Athens for the city primary key field.
1. The search starts at the root level of the . The database system
compares the value Athens with the value of the first entry in the ,
Ba.
As the value Athens is lower than Ba, the relevant address information is evaluated. This
points to an .
B* tree [Page 128]
root page [Page 103]
index page [Page 103]
2. The search continues at the index level. The value Athens is greater than the value of the
first entry in the data page, An. The next value in the page is evaluated. As the value of
Athens is smaller than the value of Au, the corresponding address information is
evaluated. This points to a
.
leaf page [Page
103]
User Manual: SAP DB 108