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									              MORE SQL: VIEWs
 Reference: Oracle Course Material, Matthew P. Johnson,
CISDD, CUNY, January, 2005




       Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-1
                      Revised by IB & SAM, Fasilkom UI, 2005
                      More SQL: Views
Stored relations physically exist and persist
Views are relations that don‟t
  in some texts, “table” = stored relation = “base
  table”
Basically names/references given to queries
  maybe a relevant subset of a table
Employee(ssn, name, department, project, salary)
      CREATE VIEW Developers AS
       SELECT name, project
       FROM Employee
       WHERE department = “Development”
Payroll has access to Employee, others only to Developers
         Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-2
                        Revised by IB & SAM, Fasilkom UI, 2005
                      A Different View
Person(name, city)
Purchase(buyer, seller, product, store)
Product(name, maker, category)

   CREATE VIEW Seattle-view AS
          SELECT buyer, seller, product, store
          FROM Person, Purchase
         WHERE Person.city = ‘Seattle’ AND
                   Person.name = Purchase.buyer
We have a new virtual table:
Seattle-view(buyer, seller, product, store)

        Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-3
                       Revised by IB & SAM, Fasilkom UI, 2005
                    A Different View
 CREATE VIEW Seattle-view AS
    SELECT buyer, seller, product, store
    FROM Person, Purchase
    WHERE Person.city = ‘Seattle’ AND
            Person.name = Purchase.buyer

Now we can query the view:
 SELECT name, store
 FROM   Seattle-view, Product
 WHERE Seattle-view.product = Product.name AND
        Product.category = ‘shoes’


      Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-4
                     Revised by IB & SAM, Fasilkom UI, 2005
    What happens when we query a view?

SELECT name, Seattle-view.store
FROM   Seattle-view, Product
WHERE Seattle-view.product = Product.name AND
         Product.category = „shoes‟

    SELECT name, Purchase.store
    FROM Person, Purchase, Product
    WHERE Person.city = ‘Seattle’ AND
           Person.name = Purchase.buyer AND
           Purchase.poduct = Product.name AND
           Product.category = ‘shoes’
       Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-5
                      Revised by IB & SAM, Fasilkom UI, 2005
            Can rename view fields



CREATE VIEW Seattle-view(seabuyer, seaseller,
                                 prod, store) AS
   SELECT buyer, seller, product, store
   FROM Person, Purchase
   WHERE Person.city = ‘Seattle’ AND
           Person.name = Purchase.buyer



       Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-6
                      Revised by IB & SAM, Fasilkom UI, 2005
                      Types of Views
Views discussed here:
  Used in databases
  Computed only on-demand – slow at runtime
  Always up to date


Sometimes talk about “materialized” views
  Used in data warehouses
  Pre-computed offline – fast at runtime

      Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-7
                     Revised by IB & SAM, Fasilkom UI, 2005
                                Updating Views
How can I insert a tuple into a table that doesn’t exist?

Employee(ssn, name, department, project, salary)

              CREATE VIEW Developers AS
               SELECT name, project
               FROM Employee
               WHERE department = ‘Development’


If we make the                      INSERT INTO Developers
following insertion:                VALUES(‘Joe’, ‘Optimizer’)


It becomes:   INSERT INTO Employee(ssn, name, department, project, salary)
              VALUES(NULL, ‘Joe’, NULL, ‘Optimizer’, NULL)
                Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-8
                               Revised by IB & SAM, Fasilkom UI, 2005
              Non-Updatable Views
Person(name, city)
Purchase(buyer, seller, product, store)

       CREATE VIEW City-Store AS
          SELECT Person.city, Purchase.store
          FROM Person, Purchase
          WHERE Person.name = Purchase.buyer

How can we add the following tuple to the view?
(„Seattle‟, „Nine West‟)
We don‟t know the name of the person who made the
purchase
cannot set to NULL (why?)
         Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-9
                        Revised by IB & SAM, Fasilkom UI, 2005
                  Indexes

 The main reference of this presentation is the textbook and
PPT from : Elmasri & Navathe, Fundamental of Database
Systems, 4th edition, 2004, Chapter 14
 Additional reference: Oracle Course Material, Matthew P.
Johnson, CISDD, CUNY, January, 2005
                   Chapter Outline
Types of Single-level Ordered Indexes
  Primary Indexes
  Clustering Indexes
  Secondary Indexes
Multilevel Indexes
Dynamic Multilevel Indexes Using B-Trees
and B+-Trees
Indexes on Multiple Keys
Index on SQL
      Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-11
                     Revised by IB & SAM, Fasilkom UI, 2005
      Indexes as Access Paths
A single-level index is an auxiliary file that makes
it more efficient to search for a record in the
data file.
The index is usually specified on one field of the
file (although it could be specified on several
fields)
One form of an index is a file of entries <field
value, pointer to record>, which is ordered by
field value
The index is called an access path on the field.

      Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-12
                     Revised by IB & SAM, Fasilkom UI, 2005
Indexes as Access Paths (contd.)
The index file usually occupies considerably less
disk blocks than the data file because its entries
are much smaller
A binary search on the index yields a pointer to
the file record
Indexes can also be characterized as dense or
sparse.
 • A dense index has an index entry for every search
   key value (and hence every record) in the data file.
 • A sparse (or nondense) index, on the other hand,
   has index entries for only some of the search values

      Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-13
                     Revised by IB & SAM, Fasilkom UI, 2005
  Indexes as Access Paths (contd.)
Example: Given the following data file:
EMPLOYEE(NAME, SSN, ADDRESS, JOB, SAL, ... )
Suppose that:
record size R=150 bytes
block size B=512 bytes
r=30000 records

Then, we get:
blocking factor Bfr= B div R= 512 div 150= 3
records/block
number of file blocks b= (r/Bfr)= (30000/3)= 10000
blocks
         Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-14
                        Revised by IB & SAM, Fasilkom UI, 2005
    Indexes as Access Paths (contd.)
For an index on the SSN field, assume the field size VSSN=9 bytes,
 assume the record pointer size PR=7 bytes. Then:
 index entry size RI=(VSSN+ PR)=(9+7)=16 bytes
 index blocking factor BfrI= B div RI= 512 div 16= 32
 entries/block
 number of index blocks b= (r/ BfrI)= (30000/32)= 938 blocks
 binary search needs log2bi= log2938= 10 block accesses

 This is compared to an average linear search cost of:
      (b/2)= 30000/2= 15000 block accesses
 If the file records are ordered, the binary search cost would be:
       log2b= log230000= 15 block accesses


            Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-15
                           Revised by IB & SAM, Fasilkom UI, 2005
    Types of Single-Level Indexes
Primary Index
  Defined on an ordered data file
  The data file is ordered on a key field
  Includes one index entry for each block in the data file;
  the index entry has the key field value for the first record
  in the block, which is called the block anchor
  A similar scheme can use the last record in a block.
  A primary index is a nondense (sparse) index, since it
  includes an entry for each disk block of the data file and
  the keys of its anchor record rather than for every search
  value.
         Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-16
                        Revised by IB & SAM, Fasilkom UI, 2005
   FIGURE
     14.1
    Primary
index on the
ordering key
 field of the
file shown in
Figure 13.7.




          Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-17
                         Revised by IB & SAM, Fasilkom UI, 2005
     Types of Single-Level Indexes
Clustering Index
  Defined on an ordered data file

  The data file is ordered on a non-key field unlike primary
  index, which requires that the ordering field of the data
  file have a distinct value for each record.

  Includes one index entry for each distinct value of the
  field; the index entry points to the first data block that
  contains records with that field value.

  It is another example of nondense index where Insertion
  and Deletion is relatively straightforward with a clustering
  index. Elmasri and Navathe, Fundamentals of Fasilkom UI, 2005 Fourth Edition
                        Revised by IB & SAM,
                                              Database Systems,                Slide 5-18
  FIGURE 14.2
A clustering index
      on the
  DEPTNUMBER
 ordering nonkey
    field of an
 EMPLOYEE file.




               Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-19
                              Revised by IB & SAM, Fasilkom UI, 2005
   FIGURE 14.3
  Clustering index
  with a separate
  block cluster for
   each group of
 records that share
the same value for
the clustering field.




           Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-20
                          Revised by IB & SAM, Fasilkom UI, 2005
     Types of Single-Level Indexes
Secondary Index
  A secondary index provides a secondary means of accessing a file for
  which some primary access already exists.
  The secondary index may be on a field which is a candidate key and has
  a unique value in every record, or a nonkey with duplicate values.
  The index is an ordered file with two fields.
   • The first field is of the same data type as some nonordering field of
     the data file that is an indexing field.
   • The second field is either a block pointer or a record pointer. There
     can be many secondary indexes (and hence, indexing fields) for the
     same file.
  Includes one entry for each record in the data file; hence, it is a dense
  index



            Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-21
                           Revised by IB & SAM, Fasilkom UI, 2005
 FIGURE 14.4
     A dense
secondary index
    (with block
 pointers) on a
nonordering key
  field of a file.




           Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-22
                          Revised by IB & SAM, Fasilkom UI, 2005
     FIGURE 14.5
     A secondary index (with
recored pointers) on a nonkey
 field implemented using one
   level of indirection so that
    index entries are of fixed
 length and have unique field
              values.




                 Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-23
                                Revised by IB & SAM, Fasilkom UI, 2005
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-24
               Revised by IB & SAM, Fasilkom UI, 2005
                Multi-Level Indexes
Because a single-level index is an ordered file, we can
create a primary index to the index itself ; in this case, the
original index file is called the first-level index and the
index to the index is called the second-level index.
We can repeat the process, creating a third, fourth, ..., top
level until all entries of the top level fit in one disk block
A multi-level index can be created for any type of first-
level index (primary, secondary, clustering) as long as the
first-level index consists of more than one disk block



          Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-25
                         Revised by IB & SAM, Fasilkom UI, 2005
FIGURE 14.6
  A two-level
 primary index
  resembling
ISAM (Indexed
  Sequential
Access Method)
 organization.




          Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-26
                         Revised by IB & SAM, Fasilkom UI, 2005
             Multi-Level Indexes

Such a multi-level index is a form of search
tree ; however, insertion and deletion of new
index entries is a severe problem because
every level of the index is an ordered file.




       Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-27
                      Revised by IB & SAM, Fasilkom UI, 2005
                      FIGURE 14.8
A node in a search tree with pointers to subtrees below it.




    Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-28
                   Revised by IB & SAM, Fasilkom UI, 2005
              FIGURE 14.9
       A search tree of order p = 3.




Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-29
               Revised by IB & SAM, Fasilkom UI, 2005
Dynamic Multilevel Indexes Using B-Trees and B+-Trees

Because of the insertion and deletion problem, most
multi-level indexes use B-tree or B+-tree data structures,
which leave space in each tree node (disk block) to allow
for new index entries
These data structures are variations of search trees that
allow efficient insertion and deletion of new search
values.
In B-Tree and B+-Tree data structures, each node
corresponds to a disk block
Each node is kept between half-full and completely full


         Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-30
                        Revised by IB & SAM, Fasilkom UI, 2005
Dynamic Multilevel Indexes Using B-Trees                                               and
               B+-Trees (contd.)
 An insertion into a node that is not full is quite efficient;
 if a node is full the insertion causes a split into two nodes
 Splitting may propagate to other tree levels
 A deletion is quite efficient if a node does not become
 less than half full
 If a deletion causes a node to become less than half full,
 it must be merged with neighboring nodes



         Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-31
                        Revised by IB & SAM, Fasilkom UI, 2005
  Difference between B-tree and B+-tree

 In a B-tree, pointers to data records exist at all levels of
the tree

 In a B+-tree, all pointers to data records exists at the
leaf-level nodes

 A B+-tree can have less levels (or higher capacity of
search values) than the corresponding B-tree



         Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-32
                        Revised by IB & SAM, Fasilkom UI, 2005
                            FIGURE 14.10
B-tree structures. (a) A node in a B-tree with q – 1 search values. (b) A
 B-tree of order p = 3. The values were inserted in the order 8, 5, 1, 7,
                               3, 12, 9, 6.
              Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-33
                             Revised by IB & SAM, Fasilkom UI, 2005
                                  FIGURE 14.11
 The nodes of a B+-tree. (a) Internal node of a B+-tree with q –1 search
values. (b) Leaf node of a B+-tree with q – 1 search values and q – 1 data
                                 pointers.
             Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-34
                            Revised by IB & SAM, Fasilkom UI, 2005
    FIGURE 14.12
An example of insertion
in a B+-tree with q = 3
      and pleaf = 2.




           Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-35
                          Revised by IB & SAM, Fasilkom UI, 2005
FIGURE 14.13
 An example of
deletion from a
   B+-tree.




         Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-36
                        Revised by IB & SAM, Fasilkom UI, 2005
     Creating Index using SQL
Single Attribute
  CREATE INDEX employee_idx ON
  EMPLOYEE(SSN);
Combination of Attribute
  CREATE INDEX employee_idx ON
  EMPLOYEE(SSN, FNAME);



      Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-37
                     Revised by IB & SAM, Fasilkom UI, 2005
                     Deleting Index
DROP INDEX Employee_idx;




    Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-38
                   Revised by IB & SAM, Fasilkom UI, 2005
                    Creating Indexes
Indexes can be useful in range queries
too: CREATE INDEX ageIndex ON Person (age)


                        SELECT *
                        FROM Person
                        WHERE age > 25




       Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-39
                      Revised by IB & SAM, Fasilkom UI, 2005
                             Using indexes
Indices can be created on multiple attributes:
                       CREATE INDEX doubleindex ON
                                      Person (age, city)


                    SELECT *
                    FROM Person
Helps in:           WHERE age = 55 AND city = „Seattle‟

                    SELECT *                                                      Idea: our sorted list
And in:             FROM Person                                                   is sorted on age;city,
                    WHERE age = 55                                                not city;age

                                                                         Q: In Movie tbl, should
But not in:         SELECT *                                             index be on year;title or
                    FROM Person                                          title;year?
                    WHERE city = „Seattle‟
          Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition               Slide 5-40
                         Revised by IB & SAM, Fasilkom UI, 2005
    Aturan/Tips Penggunaan Indeks
1. Gunakan indeks untuk tabel-tabel besar
2. Indeks key primer tiap tabel (untuk Oracle
   otomatis sudah dilakukan)
3. Indeks fields yang digunakan untuk
   pencarian record (field yang sering
   digunakan dalam klausa WHERE …)
4. Indeks field-field dalam perintah SQL
   ORDER BY … dan GROUP BY …
5. Indeks jika atribut memiliki >100 nilai
   yang mungkin, tidak jika <30 nilai
        Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-41
                       Revised by IB & SAM, Fasilkom UI, 2005
     Aturan/Tips Penggunaan Indeks

6. DBMS mungkin memiliki batas maksimum
   jumlah indeks per tabel dan jumlah byte per
   field yang diindeks
7. Nilai-nilai null tidak dapat diakses melalui
   indeks
8. Gunakan indeks sebanyak yang diperlukan
   untuk database non-volatile (jarang berubah);
   batasi penggunaan indeks untuk database
   volatile (sering berubah)
     Mengapa? Karena modifikasi (penambahan dan
     penghapusan data) akan membutuhkan
     penyusunan ulang file-file indeks
        Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition   Slide 5-42
                       Revised by IB & SAM, Fasilkom UI, 2005

								
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