oracle tables

Agenda
 Overview of Oracle Tables
 Partitioned Tables
 Clustered Tables
 Index-Organized Tables
 Compression Tables
 External Tables
 Temporary Tables

Overview of Oracle Tables
 All data of the database are stored in Tablespaces.
 Tables, Indexes, LOBs are stored as Segments and
Segments consist of Extents.
 Oracle Data Block is the smallest unit defined in the segment.
 A table definition includes a table name and set of columns.
 Each column has a data type, which is associated with a
specific storage format, constraints, and valid range of
values.
 Oracle defined lot of tables categories partitioned tables, clustered
tables, external tables, temporary tables and etc.

Partitioned Tables
 Large tables by decompose them into smaller and more manageable
pieces called partitions.
 SQL queries and DML statements do not need to be modified in order to
access partitioned tables mean partitioning is entirely transparent to
applications.
 Each partition of a table must have the same logical attributes (columns,
data types, constraints) while can have separate physical attributes like
Tablespaces.
 Improve manageability, availability and performance.
 Each row in a partitioned table is unambiguously assigned to a single
partition. The partition key is a set of one or more columns (1 to 16) that
determines the partition for each row.
 Range, List, Hash, Range-List and Range-Hash are partitioning
methods.

Clustered Tables
 Group of tables that share common columns and store related data
in the same data blocks
 Cluster key is the column or columns that the clustered tables have
in common.
 Consider clustering tables when they are primarily queried (but not
modified) and records from the tables are frequently queried
together or joined.
 Reduce Disk I/O for clustered tables joins, Less storage than non
clustered.
 Index and Hash are two cluster methods.

Index-Organized Tables
 Ordinary table has a stable physical location while IOT has no
any stable physical location.
 In IOT DML can cause an existing row to move to a different
slot, or even to a different block.
 You Can move your existing data into an index-organized
table and do all the operations you would perform in an
ordinary table.
 Secondary indexes stores logical row id instead of physical
row ids.
 Reduce Disk I/O and fast data access, Reduced storage
requirements.

Compression Tables
 The database can use table compression to reduce the
amount of storage required for the table.
 Compression saves disk space, reduces memory use in
the database buffer cache , and in some cases speeds query
execution.
 Table compression is transparent to database applications.
 There are types of compression like BASIC, OLTP.
 Can declare compression at the Tablespace, table, partition,
or sub partition level.

External Tables
 An external table accesses data in external sources as if this
data were in a table in the database.
 You could create an external table, copy the file to the
location specified in the external table definition, and use SQL
to query the records in the text file.
 Unlike an ordinary table, an external table does not describe
data stored in the database, nor does it describe how data is
stored externally.
 External tables are read-only unless created with CREATE
TABLE AS SELECT with the ORACLE_DATAPUMP access
driver. Restrictions for external tables include no support for
indexed columns, virtual columns, and column objects.

Temporary Tables
 Oracle Database temporary tables hold data that exists only
for the duration of a transaction or session.
 Data in a temporary table is private to the session, which
means that each session can only see and modify its own
data.
 The temporary table is a persistent object described in the
data dictionary, but appears empty until your session inserts
data into the table.
 Can create indexes for TT. Indexes created on temporary
tables are also temporary. Also can create temp view or
trigger too.

oracle tables

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