On the Old, the New —— 用sql语句生成语句的例子

转自：http://www.oracle.com/technology/oramag/oracle/07-may/o37plsql.html

TECHNOLOGY: PL/SQL Practices

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On the Old, the New, and ORA-22160
By Steven Feuerstein

Best practices for managing old and new information and preventing FORALL errors

I want to audit updates to a table, including the before and after values of each column in my table. To do this, I would love to pass :NEW and :OLD as arguments to procedures, but that doesn't seem to work. I'd really like to avoid hard-coding column names, because then I run into compilation issues when columns are added, dropped, or renamed. Is this possible? This is how I am currently doing things:

 

CREATE TABLE load_a ( 

a1 VARCHAR2 (10), a2 VARCHAR2 (10) ) 

/


CREATE OR REPLACE TRIGGER ins_load_a

   AFTER UPDATE

   ON scott.load_a

   FOR EACH ROW

DECLARE

   a_rec   scott.load_a%ROWTYPE;

BEGIN

   a_rec.a1 := :OLD.a1;

   a_rec.a2 := :OLD.a2;

   save_old_values (a_rec);

END;

/

The bad news is that up through Oracle Database 10g , you cannot pass :OLD and :NEW as arguments to procedures. The good news is that at least you don't have to write all the code needed to accomplish your goal.

Let's take a step back: you want to pass the old and new values available inside a trigger to a stored procedure to process the data (write the information to a log table, execute validation logic, and so on). You cannot pass :OLD and :NEW as records; instead, you must copy the individual fields of those pseudorecords to a real record that can be passed to the procedure.

It certainly is tedious and time-consuming to write that code yourself, especially for tables with many columns. Fortunately, it is quite easy to generate the code you desire.

I offer you the gen_audit_trigger_text procedure shown in Listing 1 to help you achieve your goal. I ran this program for the employees table and, after some formatting, had the resulting code shown in Listing 2.

Code Listing 1: gen_audit_trigger_text

CREATE OR REPLACE PROCEDURE gen_audit_trigger_text (

   table_in IN VARCHAR2

 , owner_in IN VARCHAR2 := USER

 , program_name_in IN VARCHAR2 := 'process_data'

)

IS

   c_rowtype           CONSTANT VARCHAR2 (100)     := table_in || '%ROWTYPE';

   l_columns            DBMS_SQL.varchar2s;


   PROCEDURE gen_copy_proc (old_or_new_in IN VARCHAR2)

   IS

   BEGIN

      DBMS_OUTPUT.put_line (   'FUNCTION copy_'

                            || old_or_new_in

                            || ' RETURN '

                            || c_rowtype

                            || ' IS l_return '

                            || c_rowtype

                            || '; BEGIN '

                           );


      FOR indx IN 1 .. l_columns.COUNT

      LOOP

         DBMS_OUTPUT.put_line (   '   l_return.'

                               || l_columns (indx)

                               || ' := '

                               || ':'

                               || old_or_new_in

                               || '.'

                               || l_columns (indx)

                               || ';'

                              );

      END LOOP;


      DBMS_OUTPUT.put_line ('RETURN l_return;');

      DBMS_OUTPUT.put_line ('END copy_' || old_or_new_in || ';');

   END gen_copy_proc;

BEGIN

   SELECT LOWER (column_name) column_name

   BULK COLLECT INTO l_columns

     FROM all_tab_columns

    WHERE owner = UPPER (owner_in) AND table_name = UPPER (table_in);


   DBMS_OUTPUT.put_line ('DECLARE');

   DBMS_OUTPUT.put_line ('   my_Old ' || table_in || '%ROWTYPE;');

   DBMS_OUTPUT.put_line ('   my_New ' || table_in || '%ROWTYPE;');

   gen_copy_proc ('old');

   gen_copy_proc ('new');

   DBMS_OUTPUT.put_line ('BEGIN');

   DBMS_OUTPUT.put_line ('   my_Old := copy_Old ();');

   DBMS_OUTPUT.put_line ('   my_New := copy_New ();');

   DBMS_OUTPUT.put_line ('   ' || program_name_in || '(my_Old, my_new);');

   DBMS_OUTPUT.put_line ('END;');

END gen_audit_trigger_text;

/

Code Listing 2: Result of gen_audit_trigger_text procedure on employees table

DECLARE

   my_old    employees%ROWTYPE;

   my_new   employees%ROWTYPE;


   FUNCTION copy_old

      RETURN employees%ROWTYPE

   IS

      l_return employees%ROWTYPE;

   BEGIN

      l_return.employee_id := :OLD.employee_id;

      l_return.first_name := :OLD.first_name;

      l_return.last_name := :OLD.last_name;

      l_return.email := :OLD.email;

      l_return.phone_number := :OLD.phone_number;

      l_return.hire_date := :OLD.hire_date;

      l_return.job_id := :OLD.job_id;

      l_return.salary := :OLD.salary;

      l_return.commission_pct := :OLD.commission_pct;

      l_return.manager_id := :OLD.manager_id;

      l_return.department_id := :OLD.department_id;

      RETURN l_return;

   END copy_old;


   FUNCTION copy_new

      RETURN employees%ROWTYPE

   IS

      l_return employees%ROWTYPE;

   BEGIN

      l_return.employee_id := :NEW.employee_id;

      l_return.first_name := :NEW.first_name;

      l_return.last_name := :NEW.last_name;

      l_return.email := :NEW.email;

      l_return.phone_number := :NEW.phone_number;

      l_return.hire_date := :NEW.hire_date;

      l_return.job_id := :NEW.job_id;

      l_return.salary := :NEW.salary;

      l_return.commission_pct := :NEW.commission_pct;

      l_return.manager_id := :NEW.manager_id;

      l_return.department_id := :NEW.department_id;

      RETURN l_return;

   END copy_new;

BEGIN

   my_old := copy_old ();

   my_new := copy_new ();

   process_data (my_old, my_new);

END;