DEFAULT COLLATION Clause

13.20 DEFAULT COLLATION Clause

Collation (also called sort ordering) determines if a character string equals, precedes, or follows another string when the two strings are compared and sorted. Oracle Database collations order strings following rules for sorted text used in different languages.

The DEFAULT COLLATION clause can appear in the following SQL statements:

Topics

Prerequisites

The COMPATIBLE initialization parameter must be set to at least 12.2.0, and MAX_STRING_SIZE must be set to EXTENDED for collation declarations to be allowed in these SQL statements.

Syntax

default_collation_clause ::=

Description of the illustration default_collation_clause.eps

collation_option ::=

Description of pseudo_collation.eps follows

Description of the illustration pseudo_collation.eps

Semantics

default_collation_clause

The default_collation_clause can appear in a package specification, a standalone type specification, and in standalone subprograms.

collation_option

The default collation of a procedure, function, package, type, or trigger must be USING_NLS_COMP. The default_collation_clause explicitly declares the default collation of a PL/SQL unit to be USING_NLS_COMP. Without this clause, the unit inherits its default collation from the effective schema default collation. If the effective schema default collation is not USING_NLS_COMP, the unit is invalid.

The effective schema default collation is determined as follows:

If the session parameter DEFAULT_COLLATION is set, the effective schema default collation is the value of this parameter. The value of the parameter can be checked by querying SYS_CONTEXT('USERENV', 'SESSION_DEFAULT_COLLATION'). The function returns NULL if DEFAULT_COLLATION is not set. The value of the parameter DEFAULT_COLLATION can be set with the statement: ALTER SESSION SET DEFAULT_COLLATION = collation_option;
If the session parameter DEFAULT_COLLATION is not set, the effective schema default collation is the declared default collation of the schema in which you create the PL/SQL unit. The default collation of a schema can be found in the static data dictionary *_USERS views. It can be set with the DDL statements CREATE USER and ALTER USER.

The session parameter DEFAULT_COLLATION can be unset with the statement: ALTER SESSION SET DEFAULT_COLLATION = NONE;

Package body and type body use the default collation of the corresponding specification. All character data containers and attributes in procedures, functions and methods, including parameters and return values, behave as if their data-bound collation were the pseudo-collation USING_NLS_COMP.

Restrictions on DEFAULT COLLATION

It cannot be specified for nested or packaged subprograms or for type methods.

Compilation Semantics

If the resulting default object collation is different from USING_NLS_COMP, the database object is created as invalid with a compilation error.

If the ALTER COMPILE statement is issued for a PL/SQL unit with the REUSE SETTINGS clause, the stored default collation of the database object being compiled is not changed.

If an ALTER COMPILE statement is issued without the REUSE SETTINGS clause, the stored default collation of the database object being compiled is discarded and the effective schema default collation for the object owner at the time of execution of the statement is stored as the default collation of the object, unless the PL/SQL unit contains the DEFAULT COLLATION clause. If the resulting default collation is not USING_NLS_COMP, a compilation error is raised.

An ALTER COMPILE statement for a package or type body references the stored collation of the corresponding specification.