v JDBC calls are translated into DB2 CLI calls through Java native methods. JDBC
requests flow from the DB2 client through DB2 CLI to the DB2 server. JDBC
cannot use static SQL.
v SQLJ applications use JDBC as a foundation for such tasks as connecting to
databases and handling SQL errors, but can also contain embedded static SQL
statements in the SQLJ source files. An SQLJ source file must be translated by
the SQLJ translator before the resulting Java source code can be compiled.
Schemas
A schema is a collection of named objects; it provides a way to group those objects
logically. A schema is also a name qualifier; it provides a way to use the same
natural name for several objects, and to prevent ambiguous references to those
objects.
For example, the schema names ’INTERNAL’ and ’EXTERNAL’ make it easy to
distinguish two different SALES tables (INTERNAL.SALES, EXTERNAL.SALES).
Schemas also enable multiple applications to store data in a single database
without encountering namespace collisions.
A schema is distinct from, and should not be confused with, an XML schema,
which is a standard that describes the structure and validates the content of XML
documents.
A schema can contain tables, views, nicknames, triggers, functions, packages, and
other objects. A schema is itself a database object. It is explicitly created using the
CREATE SCHEMA statement, with the current user or a specified authorization ID
recorded as the schema owner. It can also be implicitly created when another
object is created, if the user has IMPLICIT_SCHEMA authority.
A schema name is used as the high order part of a two-part object name. If the
object is specifically qualified with a schema name when created, the object is
assigned to that schema. If no schema name is specified when the object is created,
the default schema name is used (specified in the CURRENT SCHEMA special
register).
For example, a user with DBADM authority creates a schema called C for user A:
CREATE SCHEMA C AUTHORIZATION A
User A can then issue the following statement to create a table called X in schema
C (provided that user A has the CREATETAB database authority):
CREATE TABLE C.X (COL1 INT)
Some schema names are reserved. For example, built-in functions belong to the
SYSIBM schema, and the pre-installed user-defined functions belong to the
SYSFUN schema.
When a database is created, if it is not created with the RESTRICTIVE option, all
users have IMPLICIT_SCHEMA authority. With this authority, users implicitly
create a schema whenever they create an object with a schema name that does not
already exist. When schemas are implicitly created, CREATEIN privileges are
granted which allows any user to create other objects in this schema. The ability to
create objects such as aliases, distinct types, functions, and triggers is extended to
Java database connectivity (JDBC) and embedded SQL for Java (SQLJ) programs
Chapter 1. Concepts 3
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