Execution of DDL in PL/SQL commits TWICE: before and after the statement

You'd think that after working with Oracle Database and PL/SQL since 1990, I'd know everything.

Ha. Not so. :-)

Of course, there are always the new features, such as those coming in 12.2 (I will be blogging about those extensively in the coming months).

But even for features that have been in the language for decades, I still encounter small gaps in my knowledge.

For example, I had long known that when you execute a DDL (data definition language) statement in PL/SQL (which must be done as dynamic SQL via EXECUTE IMMEDIATE or DBMS_SQL.PARSE /EXECUTE) a commit is executed implicitly after the statement.

What I'd somehow missed was that a commit is also performed before the DDL statement is executed. So that is the point of this post:

Oracle Database issues a commit before a DDL statement is executed, and then afterwards as well.

You can see this behavior in action in the script below, which is generated from a recent PL/SQL Challenge quiz and can be run directly in LiveSQL.  All four blocks result in "Count=0" being displayed, because the effect of the DELETE is committed before the DDL statement is executed. Therefore, even when an error is raised when the DDL statement is run, the data's gone.

CREATE TABLE plch_data (n NUMBER)
/

BEGIN
   INSERT INTO plch_data
        VALUES (100);

   COMMIT;
END;
/

CREATE OR REPLACE PROCEDURE plch_show_count
IS
   l_count   INTEGER;
BEGIN
   SELECT COUNT (*) INTO l_count FROM plch_data;

   DBMS_OUTPUT.put_line ('Count=' || l_count);
END;
/

DECLARE
   l_count   INTEGER;
BEGIN
   DELETE FROM plch_data;

   EXECUTE IMMEDIATE 'create table plch_data (n number)';

   plch_show_count;
EXCEPTION
   WHEN OTHERS
   THEN
      plch_show_count;
END;
/

DECLARE
   l_count   INTEGER;
BEGIN
   DELETE FROM plch_data;

   EXECUTE IMMEDIATE 'create table plch_data2 (n number)';

   plch_show_count;
EXCEPTION
   WHEN OTHERS
   THEN
      plch_show_count;
END;
/

DECLARE
   l_count   INTEGER;
BEGIN
   DELETE FROM plch_data;

   EXECUTE IMMEDIATE 'create table plch_data (n number)';

   ROLLBACK;
   plch_show_count;
EXCEPTION
   WHEN OTHERS
   THEN
      ROLLBACK;
      plch_show_count;
END;
/

DROP TABLE plch_data2
/

DECLARE
   l_count   INTEGER;
BEGIN
   DELETE FROM plch_data;

   EXECUTE IMMEDIATE 'create table plch_data2 (n number)';

   ROLLBACK;
   plch_show_count;
EXCEPTION
   WHEN OTHERS
   THEN
      ROLLBACK;
      plch_show_count;
END;
/

DROP TABLE plch_data2
/

DROP TABLE plch_data
/

DROP PROCEDURE plch_show_count
/