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Background documentation Table Access (SELECT) Using a B* Tree Locate the document in its SAP Library structure

Table access using a B* tree is illustrated using the example of a SELECT statement.

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The address table is defined using the city primary key column. In the table, the system searches for an entry with value Athens for the city primary key field.

       1.      The search starts at the root level of the B* tree. The database system compares the value of Athens with the value of the first entry in the root page , which is Ba.

As the value of Athens is smaller than the value of Ba, the corresponding address information is evaluated. This points to an index page.

       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 Au, the corresponding address information is evaluated. This points to a leaf page.

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       3.      The search continues at the leaf level. In the position list of the leaf page a binary search algorithm is used. The corresponding address information for the table entry with the key value Athens is evaluated.

       4.      The database system scans the data section in the leaf page until it has found the corresponding table entries. The search is then complete.

 

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