ORACLE TRIM function

Question

suppose a column defined as:

col varchar2(5)

If col='X' is true;
If trim(col)=trim('X') is true;
But if col contains ' ', then if trim(col)=trim(' ') is false;

Why?

Thanks

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– Álvaro González, Commented Mar 10, 2014 at 12:48

Dmitrii Bychenko · Accepted Answer · 2014-03-11 07:00:43Z

2

Oracle doesn't support empty strings like ''; Oracle uses null instead (whenever the result should be an empty string you'll get null in fact). Since

  null = null -- <- is null (and not true)

Your formula

  trim(col) = trim(' ') -- <- equals to "null = null"

is null (and not true) too

edited Mar 11, 2014 at 7:00

answered Mar 10, 2014 at 12:39

Dmitrii Bychenko

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1 Comment

smnbbrv Over a year ago

null = null -- <- is always false - this is definitely not true. null = null returns null. Try this: declare test boolean := null = null; begin if test is null then raise program_error; end if; end;. Yes, the idea is the same: condition will not work, but it is not false!

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