Database Reference
In-Depth Information
Relational Table
. The basic structure and core of a relational data-
base, holding user data.
Object Table
. A table using an object type for its column definition,
or it can contain instances of strictly typed objects, such as type struc-
tures, collections, or binary objects.
Temporary Table
. Temporary tables are available to all sessions, but a
separate data set is temporarily available for each session using a tem-
porary table.
Index-Organized Table
. Index-Organized tables are often called
IOTs. A simple relational table, described previously, holds table data
in one physical object and index data in another physical object. For
an IOT, all columns in the table, not just the indexed columns, are
stored as a BTree index, based on the primary key. The data rows are
organized in the order of the index. This can improve performance in
some situations.
Cluster
. Used to store multiple indexes of frequently joined tables
into a single, physical object. A cluster is similar to an IOT where
more data than usual is stored with indexes, increasing data access
performance. Performance especially improves when the joined tables
are most commonly accessed together, such as in a view or join query.
A cluster is much more of an index than an IOT is and therefore is
covered in detail in Chapter 21.
External Table
. A read-only table storing data external to the data-
base, such as in a text file.
XMLType Table
. A table with an Oracle internally managed XML
datatype structure, either as the table or in a column of a table. XML
is covered in Chapter 17.
Partitioned Table
. Tables can be subdivided into partitions and sub-
partitions. Partitions are an effective performance-tuning approach
for dividing large tables on a range, list value, or hashing algorithm
basis. Partitioned tables are useful in data warehouse environments or
very large databases where parallel processing and rapid datafile
movement can be utilized.
18.1.2
Methods of Creating Tables
Tables can be created in one of three ways:
