For loop and columns in PL/SQL

Question

I am new in PL/SQL. I have a problem with loop in this language. I' d like to make loop like this:

FOR nr IN 1..102 
LOOP
  DBMS_OUTPUT.PUT_LINE(nr);
  IF rec.column_||nr IS NULL
    THEN
    DBMS_OUTPUT.PUT_LINE('test');
  END IF;
END LOOP;

I have created a cursor. As you can see I' d like to check all column with names column from column_1 to column_102. Unfortunately || operator does not work for this situation. Do you know some solution to my problem?

Answer 1

You can do this with dynamic PL/SQL . Use an EXECUTE IMMEDIATE statement to execute a string argument as PL/SQL, which you can make up with || as it was intended in the question.

Example:

BEGIN 
    FOR nr IN 1..102 
    LOOP
        DBMS_OUTPUT.PUT_LINE(nr);
        EXECUTE IMMEDIATE 
            'BEGIN ' || 
            'IF rec.column.' || nr ||' is null THEN ' ||
                'DBMS_OUTPUT.PUT_LINE(''test''); ' ||
            'END IF; ' || 
            'END; ';
    END LOOP;
END;

Or you could also assign rec.column.' || nr ||' is null rec.column.' || nr ||' is null rec.column.' || nr ||' is null to a variable and make the PUT_LINE outside the EXECUTE IMMEDIATE part:

UPDATE : It seems it is not possible to bind BOOLEAN variables, so I've modified the example to use a NUMBER .

UPDATE 2: There is a possible efficiency improvement, altough maybe not suitable in this case. Use a constant VARCHAR for the dynamic SQL, and pass in nr with a binded variable. This is even more efficient than using native SQL if in a large loop. I don't think 'rec.column.:arg is null would execute as 'rec.column.1 is null , though.

 DECLARE
    isnull NUMBER;
 BEGIN 
    FOR nr IN 1..102 
    LOOP
        DBMS_OUTPUT.PUT_LINE(nr);
        EXECUTE IMMEDIATE 
            'BEGIN ' || 
                'IF rec.column.' || nr ||' IS NULL THEN ' || 
                    ':x:=1; ' || 
                'ELSE ' ||
                    ':x:=0; ' ||
                'END IF; ' ||
            'END; ' 
            USING OUT isnull;
        IF isnull = 1 THEN 
            DBMS_OUTPUT.PUT_LINE('test');
        END IF;
    END LOOP;
END;

---

UPDATE 3 : Seeing that:

• It is not possible to access rec inside the dynamic SQL statement because it is undefined (out of scope),

• It seems not possible to pass a non-sql type as an argument to the dynamic statement (record, cursor)

A possible workaround is to bind some id columns (SQL Type) to the dynamic statement, and use a select clause to find out if the current column is null:

DECLARE
        isnull NUMBER;
        rec_id NUMBER; -- Identifier of the fetched record
     BEGIN 
        rec_id := rec.id;
        FOR nr IN 1..102 
        LOOP
            DBMS_OUTPUT.PUT_LINE(nr);
            EXECUTE IMMEDIATE 
                'SELECT 1 FROM my_table WHERE id = :idarg ' ||
                   ' AND column_' || nr || ' IS NULL'
              INTO isnull USING rec_id;
            IF isnull = 1 THEN 
                DBMS_OUTPUT.PUT_LINE('test');
            END IF;
        END LOOP;
    END;