Skip to Main Content
  • Questions

  • If one column is not null then another column should be not null, both can be nulls

Breadcrumb

Question and Answer

Tom Kyte

Thanks for the question, ravi.

Asked: June 26, 2008 - 12:45 pm UTC

Last updated: June 27, 2008 - 9:59 am UTC

Version: 10.2.0

Viewed 10K+ times! This question is

You Asked

Hi Tom,

My requirement is : If col1 is having a value then col2 should have a value and vice versa. Also the combination of col1, col2 should be unique.

Both the columns can be null.

I am trying to create a unique index on the combination of these but, I am not sure how to mention it in the index using CASE. Can you please advise.

CREATE TABLE t (col1 VARCHAR2(1),col2 NUMBER(5));

CREATE UNIQUE INDEX ix_t
ON t (CASE WHEN col1 is not null THEN col2 ELSE NULL END);

CREATE UNIQUE INDEX ix_t
ON t (CASE WHEN col2 is not null THEN col1 ELSE NULL END);

INSERT INTO t (col1, col2) VALUES (null, null);

INSERT INTO t (col1, col2) VALUES ('X', null);

Thanks,
Ravi

and Tom said...

simple check constraint, nothing fancy needed

ops$tkyte%ORA9IR2> CREATE TABLE t
  2  (col1 VARCHAR2(1),
  3   col2 varchar2(1),
  4   constraint my_check check ( (col1 is null AND col2 is null) or (col1 is not null AND col2 is not null) )
  5  );

Table created.

ops$tkyte%ORA9IR2>
ops$tkyte%ORA9IR2> INSERT INTO t (col1, col2) VALUES (null, null);

1 row created.

ops$tkyte%ORA9IR2> INSERT INTO t (col1, col2) VALUES ('X', null);
INSERT INTO t (col1, col2) VALUES ('X', null)
*
ERROR at line 1:
ORA-02290: check constraint (OPS$TKYTE.MY_CHECK) violated


ops$tkyte%ORA9IR2> INSERT INTO t (col1, col2) VALUES (null, 'X');
INSERT INTO t (col1, col2) VALUES (null, 'X')
*
ERROR at line 1:
ORA-02290: check constraint (OPS$TKYTE.MY_CHECK) violated


ops$tkyte%ORA9IR2> INSERT INTO t (col1, col2) VALUES ('X', 'X');

1 row created.

Rating

  (3 ratings)

Is this answer out of date? If it is, please let us know via a Comment

Comments

If one column is not null then another column should be not null, both can be nulls

ravi, June 27, 2008 - 9:24 am UTC

Thanks Tom, you always rock !!

I was thinking in the unique index direction. Just for learning, is it possible to implement the same using a unique index ?

Long live "Tom Kyte".

Thanks,
Ravi.
Tom Kyte
June 27, 2008 - 9:29 am UTC

using a unique index for this would not make sense - I don't see any possible connection between the rule:

c1 and c2 are either
both null
both not null

and the concept of

uniqueness


even if it "could be done", it would be the wrong way - we need not store anything extra here, we just need this rule to fire on the row - which it is - and we are done.

If one column is not null then another column should be not null, both can be nulls

ravi, June 27, 2008 - 9:48 am UTC

Hi Tom,

(sorry, overlooked the following before posting the earlier reponse).

"Also the combination of col1, col2 should be unique."

INSERT INTO t (col1, col2) VALUES ('X', 'X')
> 1 rows inserted

INSERT INTO t (col1, col2) VALUES ('X', 'X')
> 1 rows inserted

Please advise.
Thanks,
Ravi
Tom Kyte
June 27, 2008 - 9:59 am UTC

that is just then

alter table t add constraint c1_c2_unique unique(c1,c2);


If one column is not null then another column should be not null, both can be nulls

ravi, June 27, 2008 - 10:36 am UTC

Thanks Tom, much appreciated.

Long live "Tom Kyte".
more

Connor and Chris don't just spend all day on AskTOM. You can also catch regular content via Connor's blog and Chris's blog. Or if video is more your thing, check out Connor's latest video and Chris's latest video from their Youtube channels. And of course, keep up to date with AskTOM via the official twitter account.