Come generare istruzioni DELETE in PL/SQL, in base alle relazioni FK delle tabelle?

(La mia prima risposta è diventata troppo lunga e difficile da modificare, ed è diventata Community Wikified, il che è davvero fastidioso. Ecco l'ultima versione dello script.)

Questo script tenta di eseguire un'eliminazione a cascata tramite ricorsione. Dovrebbe evitare loop infiniti quando ci sono riferimenti circolari. Ma richiede che tutti i vincoli referenziali circolari abbiano ON DELETE SET NULL o ON DELETE CASCADE .

CREATE OR REPLACE PROCEDURE delete_cascade(
    table_owner          VARCHAR2,
    parent_table         VARCHAR2,
    where_clause         VARCHAR2
) IS
    /*   Example call:  execute delete_cascade('MY_SCHEMA', 'MY_MASTER', 'where ID=1'); */

    child_cons     VARCHAR2(30);
    parent_cons    VARCHAR2(30);
    child_table    VARCHAR2(30);
    child_cols     VARCHAR(500);
    parent_cols    VARCHAR(500);
    delete_command VARCHAR(10000);
    new_where_clause VARCHAR2(10000);

    /* gets the foreign key constraints on other tables which depend on columns in parent_table */
    CURSOR cons_cursor IS
        SELECT owner, constraint_name, r_constraint_name, table_name, delete_rule
          FROM all_constraints
         WHERE constraint_type = 'R'
           AND delete_rule = 'NO ACTION'
           AND r_constraint_name IN (SELECT constraint_name
                                       FROM all_constraints
                                      WHERE constraint_type IN ('P', 'U')
                                        AND table_name = parent_table
                                        AND owner = table_owner)
           AND NOT table_name = parent_table; -- ignore self-referencing constraints


    /* for the current constraint, gets the child columns and corresponding parent columns */
    CURSOR columns_cursor IS
        SELECT cc1.column_name AS child_col, cc2.column_name AS parent_col
          FROM all_cons_columns cc1, all_cons_columns cc2
         WHERE cc1.constraint_name = child_cons
           AND cc1.table_name = child_table
           AND cc2.constraint_name = parent_cons
           AND cc1.position = cc2.position
        ORDER BY cc1.position;
BEGIN
    /* loops through all the constraints which refer back to parent_table */
    FOR cons IN cons_cursor LOOP
        child_cons   := cons.constraint_name;
        parent_cons  := cons.r_constraint_name;
        child_table  := cons.table_name;
        child_cols   := '';
        parent_cols  := '';

        /* loops through the child/parent column pairs, building the column lists of the DELETE statement */
        FOR cols IN columns_cursor LOOP
            IF child_cols IS NULL THEN
                child_cols  := cols.child_col;
            ELSE
                child_cols  := child_cols || ', ' || cols.child_col;
            END IF;

            IF parent_cols IS NULL THEN
                parent_cols  := cols.parent_col;
            ELSE
                parent_cols  := parent_cols || ', ' || cols.parent_col;
            END IF;
        END LOOP;

        /* construct the WHERE clause of the delete statement, including a subquery to get the related parent rows */
        new_where_clause  :=
            'where (' || child_cols || ') in (select ' || parent_cols || ' from ' || table_owner || '.' || parent_table ||
            ' ' || where_clause || ')';

        delete_cascade(cons.owner, child_table, new_where_clause);
    END LOOP;

    /* construct the delete statement for the current table */
    delete_command  := 'delete from ' || table_owner || '.' || parent_table || ' ' || where_clause;

    -- this just prints the delete command
    DBMS_OUTPUT.put_line(delete_command || ';');

    -- uncomment if you want to actually execute it:
    --EXECUTE IMMEDIATE delete_command;

    -- remember to issue a COMMIT (not included here, for safety)
END;