Oracle – Building a Conditional Check Constraint

check-constraintsoracle

I'm trying to build a conditional check constraint for my table TBL_AFIL, which has two fields:

Fec_Renun DATE
flg_afil INTEGER

Constraint: IF flg_afil=1 THEN Fec_Renun can not be NULL.

ALTER TABLE TBL_AFIL
ADD CONSTRAINT FecRenun_Not_Null CHECK (Fec_Renun IS not NULL and flg_afil =1) ;

But it throws this error:

ORA-02293: cannot validate (FecRenun_Not_Null) - check constraint violated

But when I run this query, it returns 0 rows.

SELECT * FROM TBL_AFIL
WHERE FEC_RENUN IS NULL
AND FLG_AFIL =1;

I know that to this constraint I could add ENABLE NOVALIDATE, but I'm intrigued why can't build this constraint.

Best Answer

CHECK (NOT (flag_afil = 1 AND fec_renum IS NULL))

Related Solutions

Oracle – How to Get Meaningful Second String in ORA-02296 Error

Provide a name for the constraint:

SQL> create table monkey(tail_count number);

Table created.

SQL> insert into monkey values (null);

1 row created.

SQL> alter table monkey modify tail_count not null;
alter table monkey modify tail_count not null
*
ERROR at line 1:
ORA-02296: cannot enable (ANIMAL.) - null values found

SQL> alter table monkey modify tail_count constraint tail_count_not_null not null;
alter table monkey modify tail_count constraint tail_count_not_null not null
                                                *
ERROR at line 1:
ORA-02296: cannot enable (ANIMAL.TAIL_COUNT_NOT_NULL) - null values found

PostgreSQL – Enforce NOT NULL with CHECK Constraint for New Rows

Mark all your existing rows as old:

ALTER TABLE integrations.billables
ADD COLUMN is_old BOOLEAN NOT NULL DEFAULT false;

UPDATE integrations.billables SET is_old = true;

And set up the constraint to ignore old rows:

ALTER TABLE integrations.billables
ADD CONSTRAINT cc_at_least_one_mapping_needed_billables 
CHECK (
    NOT(("qb_id", "xero_id", "freshbooks_id", "unleashed_id", "csv_data", "myob_id") IS NULL)
    OR is_old
);

(Yes, that IS NULL check works. See here.)

Advantages of this mechanism:

Constraint remains valid
You can continue to update old rows without filling in this value

Downsides:

A similar situation down the road will be messy. You would have to add a second boolean column or some other hoop jumping for the second new column.
If you want to force updated rows to be given a value, this won't do it.
This has the potential for abuse, since someone could just flip the is_old flag to true. (This can be addressed, though. See below.) This isn't something to be concerned about if end users can't access the database directly and you can trust the developers not to do wacky things with the data.

If you are worried about somebody changing the flag, you could set up a trigger to prevent any inserts or updates from setting is_old to true:

CREATE FUNCTION throw_error_on_illegal_old()
  RETURNS trigger
  LANGUAGE plpgsql
  AS $$
  BEGIN
    IF NEW.is_old THEN
      -- Need to make sure we don't try to access
      -- OLD in an INSERT
      IF TG_OP = 'INSERT' THEN
        RAISE 'Cannot create new with is_old = true';
      ELSE
        IF NOT OLD.is_old THEN
          RAISE 'Cannot change is_old from false to true';
        END IF;
      END IF;
    END IF;
    -- If we get here, all tests passed
    RETURN NEW;
  END
  $$
;

CREATE TRIGGER billables_prohibit_marking_row_old
BEFORE INSERT OR UPDATE ON integrations.billables
FOR EACH ROW EXECUTE PROCEDURE throw_error_on_illegal_old()
;

You do still have to trust that no one who can modify the database schema is going to come along and drop your trigger or something, but if they're going to do that, they could drop the constraint, too.

Here's a SQLFiddle demo. Note that the "should skip" row is not in the output (as we desired).

Best Answer

Related Solutions

Oracle – How to Get Meaningful Second String in ORA-02296 Error

PostgreSQL – Enforce NOT NULL with CHECK Constraint for New Rows

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