Nested Cursors in PL/SQL

Question

I am working with Oracle PL/SQL. I´m trying to define Nested Cursors, which means that the output from the first Cursor should be the input for the second. To be more specific: the first one should store tables with a specific prefix in it. The second one should store all values from an attribute from all the tables which are in the first one.

Here is my code snippet. I hope it makes my problem a little more clear:

DECLARE
    var_table_name  VARCHAR2(30);
    var_dimension_key  VARCHAR2(30);

CURSOR cur_all_dim IS  
    SELECT 
        table_name
        FROM  dba_tables
        WHERE dba_tables.tablespace_name = 'USERS'
        AND dba_tables.owner = 'DWH_CORE'
        AND UPPER (dba_tables.table_name) LIKE ('%DIM%%')
        AND UPPER (dba_tables.table_name) NOT LIKE ('%TEMP%')
        AND UPPER (dba_tables.table_name) NOT LIKE ('%DEBUG%')
        AND UPPER (dba_tables.table_name) NOT LIKE ('%LOG%');

CURSOR cur_dimension_key IS
    SELECT dimension_key FROM var_table_name;


BEGIN
OPEN cur_all_dim;

LOOP
EXIT WHEN cur_all_dim%NOTFOUND;

    FETCH cur_all_dim INTO var_table_name;

    OPEN cur_dimensions_key;
    LOOP
    EXIT WHEN cur_dimensions_key%NOTFOUND;
    FETCH cur_dimensions_key INTO var_dimension_key;
    dbms_output.put_line (var_table_name);
    dbms_output.put_line (var_dimension_key);


    END LOOP;
    CLOSE cur_dimension_key;
END LOOP;
CLOSE cur_all_dim;
END;

Answer 1

Static cursors can only access static objects. In other words, static cursors work only if all tables and columns are known at compile time.

If you need to access a table whose name will only be known during execution, you'll have to use dynamic SQL. For instance, you could use a REF CURSOR in your case:

DECLARE
   var_table_name    VARCHAR2(30);
   var_dimension_key VARCHAR2(30);
   cur_dimension_key SYS_REFCURSOR;
BEGIN
   FOR cur_all_dim IN (SELECT table_name
                         FROM dba_tables
                        WHERE dba_tables.tablespace_name = 'USERS'
                          AND dba_tables.owner = 'DWH_CORE'
                          AND UPPER(dba_tables.table_name) LIKE ('%DIM%%')
                          AND UPPER(dba_tables.table_name) NOT LIKE ('%TEMP%')
                          AND UPPER(dba_tables.table_name) NOT LIKE ('%DEBUG%')
                          AND UPPER(dba_tables.table_name) NOT LIKE ('%LOG%')) 
   LOOP      
      OPEN cur_dimension_key 
       FOR 'SELECT dimention_key 
              FROM ' || cur_all_dim.table_name;
      LOOP
         FETCH cur_dimensions_key INTO var_dimension_key;
         EXIT WHEN cur_dimensions_key%NOTFOUND;
         dbms_output.put_line(cur_all_dim.table_name);
         dbms_output.put_line(var_dimension_key);      
      END LOOP;
      CLOSE cur_dimension_key;
   END LOOP;
END;

Answer 2

    create or replace PROCEDURE PROC_NESTED_CURSOR 
    AS 
    CUR1 SYS_REFCURSOR;
    CUR2 SYS_REFCURSOR;
    LV_DEPTID NUMBER;
    LV_DEPTNAME VARCHAR2(200);
    LV_EMPID NUMBER;
    LV_FSTNAME VARCHAR2(200);
    LV_SALARY NUMBER(8,2);
    LV_JOBID VARCHAR2(20);
    BEGIN
      OPEN CUR1 FOR 
        select department_id, department_name from departments;

      LOOP 
        FETCH CUR1 INTO LV_DEPTID,LV_DEPTNAME; 
        EXIT WHEN CUR1%NOTFOUND;    
        dbms_output.put_line('                                                                                                   ');
        dbms_output.put_line('DEPARTMENT ID  '||LV_DEPTID ||'                               '|| 'DEPARTMENT NAME  '||LV_DEPTNAME);
        dbms_output.put_line('---------------------------------------------------------------------------------------------------');
        dbms_output.put_line(RPAD('EMPLOYEE NUMBER',20)||RPAD('EMPLOYEE NAME',20) ||RPAD('SALARY',20)||RPAD('JOB',20) );
          OPEN CUR2 FOR SELECT EMPLOYEE_ID,FIRST_NAME,SALARY,JOB_ID FROM EMPLOYEES WHERE DEPARTMENT_ID = LV_DEPTID;
          LOOP 
            FETCH CUR2 INTO LV_EMPID,LV_FSTNAME,LV_SALARY,LV_JOBID;
            EXIT WHEN CUR2%NOTFOUND;
             dbms_output.put_line(RPAD( LV_EMPID,20)|| RPAD(LV_FSTNAME,20)||RPAD(LV_SALARY,20)||LV_JOBID);

            END LOOP;
       END LOOP; 
    END PROC_NESTED_CURSOR;

/**This will print like this:-
    Department Number :10               Department Name : XXXX
    ________________________________________________________
    EMPLOYEE NUMBER    EMPLOYEE NAME      SALARY         JOB

    XXXXXX                  XXXXXX                  XXXX            XXXXX
    XXXXXX                  XXXXXX                  XXXX            XXXXX
    .........

**/