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7.1. DB2 Database Objects: The Big Picture
A database is a collection of database objects, and you can create it in one or more database partitions. A database partition, as its name implies, is part of a database. We discuss these concepts in more detail in the next sections; for now, we introduce you to the DB2 database objects. Table spaces are logical objects that associate tables and indexes to the physical devices where these objects are stored, as well as to the physical memory where the data in these objects is cached. Tables and indexes must be created inside a table space as illustrated in Tables consist of rows and columns, like spreadsheets. Data can be inserted, deleted, and updated within a table. buffer pool is an area in physical memory that caches the database information most recently used. Without buffer pools, every single piece of data has to be retrieved from disk, which is very slow. Buffer pools are associated to tables and indexes through a table space. In view is an alternate way of representing data that exists in one or more tables. A view can include some or all of the columns from one or more tables. It can also be based on other views. In Figure 7.1, view v1 is based on table t1. The first part of this two-part name is the schema name. A schema is an object that provides a logical grouping of other database objects. A schema can be owned by an individual who can control access to the objects within it. Schemas can be implicitly or explicitly specified when accessing an object.
schema_name.object_name
Figure 7.1. An overview of the DB2 database objects
- CREATE
- DECLARE
- ALTER
- DROP
The following objects can be created and dropped using the CREATE and DROP statements, respectively:
- Tables
- Indexes
- Schemas
- Views
- User-defined functions
- User-defined types
- Buffer pools
- Table spaces
- Stored procedures
- Triggers
- Servers (for federated databases)
- Wrappers (for federated databases)
- Nicknames (for federated databases)
- Sequences
You use the DECLARE statement to create temporary tables, and the ALTER statement to change one or more characteristics of an existing database object. You can alter most, but not all, of the database objects created with the CREATE statement.The CREATE, DECLARE, ALTER , and DROP statements are used throughout this chapter.
