Nested Subprograms

Subprograms created in a PL/SQL block include sub-stored-procedures or subfunctions declared and created in anonymous blocks, stored procedures, functions, and stored procedures and functions in packages.

Precautions

This is used in the ORA compatibility database.
The maximum number of nesting layers is specified by the max_subpro_nested_layers parameter. The default value is 3, and the value range is 0 to 100. If a nested subprogram contains an anonymous block, the layer of anonymous block is not counted, but the nested subprograms in the anonymous block are counted in the total number of layers.
Nested subprograms do not support reloading or SETOF.
Nested subprograms cannot be defined as autonomous transactions. They can call stored procedures or functions that contain autonomous transactions.
Subfunctions (FUNCTION) cannot be directly called and must have return values. Sub-stored-procedures (PROCEDURE) cannot be called in expressions.
Nested subprograms cannot be called by PERFORM. Dynamic statements cannot contain nested subprograms.

Currently, only the following modifiers are supported for nested subprograms:

{IMMUTABLE  | STABLE  | VOLATILE }  
{CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT }

Only one qualifier can reference a nested subprogram or a variable of a nested subprogram.
When the return value type of a subfunction (FUNCTION) is the record type customized by the function, subfunc().col cannot be used to access the column attribute of the return value of the subfunction. As a result, an error is reported during execution.
The declaration of a nested subprogram must be at the end of the declaration part (declare the nested subprogram after the declaration of variables, cursors, and types is complete).
Nested subprograms can be called only inside declared functions or stored procedures and cannot be used externally.
The debugger breakpoint is not supported when nested subprograms are used. Step-by-step debugging is supported.
Other precautions are the same as those for stored procedures and functions.

Syntax

Syntax format for creating a sub-stored-procedure:

      
           PROCEDURE procedure_name [ (parameters) ]
    [{IMMUTABLE  | STABLE  | VOLATILE }
     | {CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT }]
    { IS | AS }
    [ declarations ]
BEGIN
    plsql_body
END;

Syntax for creating a subfunction:

      
           FUNCTION function_name  [ (parameters) ] RETURN rettype     
    [{IMMUTABLE  | STABLE  | VOLATILE }
     | {CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT }]
    { IS | AS }
    [ declarations ]
BEGIN
    plsql_body
END;

In the declarations part, you can define the nested subprograms of the lower layer.

Example:

      
       
         
         
           -- Create a stored procedure.
CREATE OR REPLACE PROCEDURE proc_test() AS
    -- Declare and define a sub-stored-procedure.
    PROCEDURE proc_sub() IS
    BEGIN
        dbe_output.put_line('this is subpragram');
    END;
BEGIN
    dbe_output.put_line('this is a procedure');
    -- Call a sub-stored-procedure in an execution block.
    proc_sub();
END;
/
    -- Call a stored procedure externally.
BEGIN
    proc_test;
END;
/
-- Output the result.
this is a procedure
this is subpragram
ANONYMOUS BLOCK EXECUTE

          

        

      
     

Declaration and Definition Rules of Nested Subprograms

Nested subprograms cannot be declared or defined repeatedly. Reloading is not supported.
The identifier of a nested subprogram cannot be the same as the variable name or keyword.
Declaration before definition is supported. The definition of subprogram declared first must be found in the subsequent declaration block.

Calling Rules of Nested Subprograms

Nested subprograms can call themselves to achieve recursive calling effects.
Nested subprograms can call upper-layer subprograms.
Nested subprograms can call locally declared lower-layer subprograms, but cannot call nested subprograms in lower-layer subprograms.
Nested subprograms can call subprograms declared earlier than themselves at the same layer.

Example:

     
      
        
        
          -- Call itself.
CREATE OR REPLACE PROCEDURE proc_test(var1 int) AS
    PROCEDURE proc_sub(var2 int) IS
    BEGIN
        dbe_output.put_line('var = ' || var2);
        IF var2 > 1 THEN
            proc_sub(var2 - 1);
        END IF;
    END;
BEGIN
    proc_sub(var1);
END;
/
BEGIN
    proc_test(3);
END;
/
-- Output the result.
var = 3
var = 2
var = 1

-- Call the upper-layer subprogram.
CREATE OR REPLACE PROCEDURE proc_test(var1 int) AS
    PROCEDURE procsub_1(var2 int) IS
    BEGIN
	proc_test(var2 - 1);
    END;
BEGIN
    dbe_output.put_line('proc_test var1 = ' || var1);
	IF var1 > 1 THEN
	      procsub_1(var1);
	END IF;
END;
/
BEGIN
    proc_test(3);
END;
/
-- Output the result.
proc_test var1 = 3
proc_test var1 = 2
proc_test var1 = 1

-- Call the lower-layer subprogram declared locally.
CREATE OR REPLACE PROCEDURE proc_test() AS
    PROCEDURE proc_sub1 IS
        procedure proc_sub2 IS
        BEGIN
            dbe_output.put_line('--this is subpragram2 begin');
            dbe_output.put_line('--this is subpragram2 end');
        END;
    BEGIN
	dbe_output.put_line('this is subpragram1 begin');
	proc_sub2();
	dbe_output.put_line('this is subpragram1 end');
    END;
BEGIN
    dbe_output.put_line('this is a procedure begin');
    proc_sub1();
    dbe_output.put_line('this is a procedure end');
END;
/
BEGIN
    proc_test;
END;
/
-- Output the result.
this is a procedure begin
this is subpragram1 begin
--this is subpragram2 begin
--this is subpragram2 end
this is subpragram1 end
this is a procedure end

         

       

     
    

Variables of Nested Subprograms

Variable types include basic types and cursor types supported by PL/SQL.

Accessible variables:
- Variable declared by itself.
- Variable declared by the upper-layer subprogram.
Variable access rules:
- If a variable does not contain a qualifier, the variable is first searched in the program. If the variable name does not exist, the variable is searched at the upper layer, and so on.
- If a variable has a qualifier, it is searched in the area of the qualifier. Currently, only one qualifier can be called.