Aliases

An alias can be thought of as an alternative name for a table, partition of a table, view, or member of a database file. A table or view in an SQL statement can be referenced by its name or by an alias. An alias can only refer to a table, partition of a table, view, or database file member within the same relational database.

An alias can be used wherever a table or view name can be used, except:

• Do not use an alias name where a new table or view name is expected, such as in the CREATE TABLE or CREATE VIEW statements. For example, if an alias name of PERSONNEL is created, then a subsequent statement such as CREATE TABLE PERSONNEL will cause an error.
• An alias that refers to an individual partition of a table or member of a database file can only be used in a select statement, CREATE INDEX, DELETE, INSERT, SELECT INTO, SET variable, UPDATE, or VALUES INTO statement.

Aliases can also help avoid using file overrides. Not only does an alias perform better than an override, but an alias is also a permanent object that only need be created once.

An alias can be created even though the object that the alias refers to does not exist. However, the object must exist when a statement that references the alias is executed. A warning is returned if the object does not exist when the alias is created. An alias cannot refer to another alias. An alias can only refer to a table, partition of a table, view, or database file member within the same relational database.

The option of referring to a table, partition of a table, view, or database file member by an alias name is not explicitly shown in the syntax diagrams or mentioned in the description of the SQL statements.

A new alias cannot have the same fully-qualified name as an existing table, view, index, file, or alias.

The effect of using an alias in an SQL statement is similar to that of text substitution. The alias, which must be defined before the SQL statement is executed, is replaced by the qualified base table, partition of a table, view, or database file member name. For example, if PBIRD.SALES is an alias for DSPN014.DIST4_SALES_148, then at statement run time:

   SELECT * FROM PBIRD.SALES

effectively becomes

   SELECT * FROM DSPN014.DIST4_SALES_148

The effect of dropping an alias and recreating it to refer to another table depends on the statement that references the alias.

• SQL Data or SQL Data Change statements that refer to that alias will be implicitly rebound when they are next run.
• If a CREATE VIEW or CREATE INDEX statement refers to an alias, dropping and re-creating the alias has no effect on the view or index.

For syntax toleration of existing DB2 UDB for z/OS applications, SYNONYM can be used in place of ALIAS in the CREATE ALIAS and DROP ALIAS statements.