DB2 10.5 for Linux, UNIX, and Windows

Grouping objects by schema

Database object names might be made up of a single identifier or they might be schema-qualified objects made up of two identifiers. The schema, or high-order part, of a schema-qualified object provides a means to classify or group objects in the database. When an object such as a table, view, alias, distinct type, function, index, package or trigger is created, it is assigned to a schema. This assignment is done either explicitly or implicitly.

Explicit use of the schema occurs when you use the high-order part of a two-part object name when referring to that object in a statement. For example, USER A issues a CREATE TABLE statement in schema C as follows:

   CREATE TABLE C.X (COL1 INT)

Implicit use of the schema occurs when you do not use the high-order part of a two-part object name. When this happens, the CURRENT SCHEMA special register is used to identify the schema name used to complete the high-order part of the object name. The initial value of CURRENT SCHEMA is the authorization ID of the current session user. If you want to change this during the current session, you can use the SET SCHEMA statement to set the special register to another schema name.

Some objects are created within certain schemas and stored in the system catalog tables when the database is created.

You do not have to explicitly specify in which schema an object is to be created; if not specified, the authorization ID of the statement is used. For example, for the following CREATE TABLE statement, the schema name defaults to the authorization ID that is currently logged on (that is, the CURRENT SCHEMA special register value):

    CREATE TABLE X (COL1 INT)

Dynamic SQL and XQuery statements typically use the CURRENT SCHEMA special register value to implicitly qualify any unqualified object name references.

Before creating your own objects, you must consider whether you want to create them in your own schema or by using a different schema that logically groups the objects. If you are creating objects that will be shared, using a different schema name can be very beneficial.