PL/SQL Dynamic SQL : Table name not valid - sql

Question

I'm currently learning PL/SQL. I need to create a PL/SQL block to create a backup of all my tables like this : myTable -> myTable_old.
Here's what I got right now :
DECLARE
Cursor c IS SELECT table_name
FROM user_tables
WHERE table_name NOT LIKE '%_old';
sql_slc VARCHAR2(200);
sql_drp VARCHAR2(200);
sql_crt VARCHAR2(200);
row_count NUMBER;
t_name user_tables.table_name%type;
t_backup_name user_tables.table_name%type;
BEGIN
sql_drp := 'DROP TABLE :1 CASCADE';
sql_crt := 'CREATE TABLE :1 AS SELECT * FROM :2';
sql_slc := 'SELECT COUNT(*) FROM user_tables WHERE table_name = :1';
OPEN c;
LOOP
FETCH c INTO t_name;
EXIT WHEN (c%NOTFOUND);
t_backup_name := t_name || '_old';
dbms_output.put_line(t_name || ' ' || t_backup_name);
EXECUTE IMMEDIATE sql_slc INTO row_count USING t_backup_name;
IF row_count > 0 THEN
dbms_output.put_line(t_backup_name || ' dropped');
EXECUTE IMMEDIATE sql_drp USING t_backup_name;
END IF;
dbms_output.put_line(t_backup_name || ' created');
EXECUTE IMMEDIATE sql_crt USING t_backup_name, t_name;
COMMIT;
END LOOP;
CLOSE c;
END;
/
Here's the error :
OUVRAGE OUVRAGE_old
OUVRAGE_old created
DECLARE
*
ERROR on line 1 :
ORA-00903: table name not valid
ORA-06512: on line 29
I don't understand why this error is coming up, can someone help me ?

Answer 1

The issue is that you can not use bind variables for table names; Oracle documentation:
The database uses the values of bind variables exclusively and does
not interpret their contents in any way.
You should edit your code to use concatenation instead:
DECLARE
Cursor c IS SELECT table_name
FROM user_tables
WHERE table_name NOT LIKE '%_OLD'; /* OLD, upper case */
sql_slc VARCHAR2(200);
--sql_drp VARCHAR2(200);
--sql_crt VARCHAR2(200);
row_count NUMBER;
t_name user_tables.table_name%type;
t_backup_name user_tables.table_name%type;
BEGIN
-- sql_drp := 'DROP TABLE :1 CASCADE';
-- sql_crt := 'CREATE TABLE :1 AS SELECT * FROM :2';
sql_slc := 'SELECT COUNT(*) FROM user_tables WHERE table_name = :1';
OPEN c;
LOOP
FETCH c INTO t_name;
EXIT WHEN (c%NOTFOUND);
t_backup_name := t_name || '_OLD'; /* OLD, upper case */
DBMS_OUTPUT.put_line (t_name || ' ' || t_backup_name);
EXECUTE IMMEDIATE sql_slc INTO row_count USING t_backup_name;
IF row_count > 0
THEN
DBMS_OUTPUT.put_line (t_backup_name || ' dropped');
-- EXECUTE IMMEDIATE sql_drp USING t_backup_name;
EXECUTE IMMEDIATE ' drop table ' || t_backup_name; /* concatenation and not bind variables */
END IF;
DBMS_OUTPUT.put_line (t_backup_name || ' created'); /* concatenation and not bind variables */
-- EXECUTE IMMEDIATE sql_crt USING t_backup_name, t_name;
EXECUTE IMMEDIATE 'create table ' || t_backup_name || ' as select * from ' || t_name;
COMMIT;
END LOOP;
CLOSE c;
END;
Also, notice that, if not double quoted, object names always are uppercase, so you have to look for t_name || '_OLD' and not t_name || '_old'