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Editorial Team
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Asked: 2026-05-12T08:17:08+00:00

Apparently oracle doesn’t seem to distinguish between empty strings and nulls. E.g. Select name

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Apparently oracle doesn’t seem to distinguish between empty strings and nulls. E.g. 

Select name from TABLE_A where id=100;
  ID   NAME
  100  null

Update TABLE_A set NAME='' where id=100;
SELECT -->
  ID   NAME
  100  null

SELECT length(NAME) FROM TABLE_A WHERE id=100;
  null

I can’t think of any good reason why Oracle would be built to behave this way (does it do this in sqlplus as well?-I’m accessing through a java interface, the article referenced used a php client).

Wouldn’t you at least want to distinguish 0 length from undefined length? Is this a known issue? Intentional behavior for some specific purpose? A long-running dispute in database theory? What gives?

(This was prompted by Matt Solnit’s answer to this question.)

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1 Answer

  1. Editorial Team

    Oracle is very very very old.

    Back in 80's when it was developed (and before there were any standards) they thought is was a good idea, and given then way Oracle stores its values, it really was.

    Here’s how Oracle stores data (taken from the documentation):

    alt text

    No datatype is stored within the data, only the data length and the data itself.

    If the NULL occurs between two columns with values, it’s stored as a single byte meaning column has length 0 (actually, 0xFF). Trailing NULLs are not stored at all.

    So to store the value 'test', Oracle needs to store 5 bytes: 04 74 65 73 74.

    However, to store both an empty string and a NULL, Oracle just needs to set data length to 0.

    Very smart if your data are to be stored on 20 Mb hard drives that cost 5,000$ each.

    Later, when the standards appeared, it wasn’t such a good idea anymore, but by that time there already were lots and lots of code relying on NULL and '' being the same thing.

    Making VARCHAR to do such a distinction will break tons of code.

    To fix it, they renamed VARCHAR to VARCHAR2 (which is not a part of any standard), stated that VARCHAR2 will never distinguish between a NULL and an empty string and urged everybody to use this datatype instead.

    Now they are probably waiting for the last person who used a VARCHAR in Oracle database to die.

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