Understanding Capture

--separated chain of identifiers,

--including schema name used as

--scope qualifier followed by package

--name used as scope qualifier

--followed by function name)

--followed by component selector

--of the returned result followed

--by indexing followed by component

--selector

n := scott.pkg1.f1.n;

--(10) dot-separated chain of identifiers

--(schema name used as scope qualifier

--followed by package name also used

--as scope qualifier followed by

--function name also used as scope

--qualifier followed by local

--variable name)

...

END f1;

FUNCTION f2 (q1 NUMBER) RETURN t2 IS BEGIN

...

END f2; END pkg1;

Differences in Name Resolution Between SQL and PL/SQL

When the PL/SQL compiler processes a SQL statement, such as a DML statement, it uses the same name-resolution rules as SQL. For example, for a name such as SCOTT.FOO, SQL matches objects in the SCOTT schema first, then packages, types, tables, and views in the current schema.

PL/SQL uses a different order to resolve names in PL/SQL statements such as assignments and procedure calls. In the case of a name SCOTT.FOO, PL/SQL searches first for packages, types, tables, and views named SCOTT in the current schema, then for objects in the SCOTT schema.

Understanding Capture

When a declaration or type definition in another scope prevents the compiler from resolving a reference correctly, that declaration or definition is said to "capture" the reference. Usually this is the result of migration or schema evolution. There are three kinds of capture: inner, same-scope, and outer. Inner and same-scope capture apply only in SQL scope.

Inner Capture

An inner capture occurs when a name in an inner scope no longer refers to an entity in an outer scope:

■The name might now resolve to an entity in an inner scope.

■The program might cause an error, if some part of the identifier is captured in an inner scope and the complete reference cannot be resolved.

If the reference points to a different but valid name, you might not know why the program is acting differently.

How PL/SQL Resolves Identifier Names D-3