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From:Mark Richards Date:September 15 2003 3:29pm
Subject:RE: Does NULL == ""?
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I ran into the issue where data had been written, and then a Null was
written.

The presence of Null in a field may not in fact guarantee that data has
never been written.

-m-


-----Original Message-----
From: Alec.Cawley@stripped [mailto:Alec.Cawley@stripped] 
Sent: Monday, September 15, 2003 11:12
To: rchrismon%patmedia.net%QUANTELWEB%QUANTELCOMMS@stripped
Cc: mysql@stripped
Subject: Re: Does NULL == ""?


No, NULL is not the same as the empty string. NULL, for any class of field,
means that no data has ever been written there. Tests involving NULL other
than IS NULL and IS NOT NULL will return NULL. Thus "" < "a" returns 1
(true) whereas NULL < "a" returns NULL, which will always be regarded as a
"miss" in any select.




|---------+---------------------------->
|         |           "Randy Chrismon" |
|         |           <rchrismon@patmed|
|         |           ia.net>          |
|         |                            |
|         |           15/09/2003 16:00 |
|         |                            |
|---------+---------------------------->
 
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  |       Subject:  Does NULL == ""?
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The MySQL documentation confuses me a bit. If I create a table with
property NOT NULL and default "", does that mean that a record with a
column so defined will have a zero-length string in that column if I
don't provide a value? I guess what I'm asking is whether there's a
difference between a field with NULL in it and a field with a
zero-length ("") string in it.

Thanks.

Randy

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Thread
Does NULL == ""?Randy Chrismon15 Sep
  • Re: Does NULL == ""?Bruce Feist15 Sep
  • RE: Does NULL == ""?Mark Richards15 Sep
  • Re: Does NULL == ""?Brent Baisley15 Sep
    • Re: Does NULL == ""?Keith C. Ivey15 Sep
  • Re: Does NULL == ""?Paul DuBois15 Sep
Re: Does NULL == ""?Alec.Cawley15 Sep
  • RE: Does NULL == ""?Mark Richards15 Sep
Re: Does Null == ""?Randy Chrismon15 Sep
  • RE: Does Null == ""?Mark Richards15 Sep
  • Re: Does Null == ""?Bob Hall16 Sep
    • Re: Does Null == ""?Bruce Feist16 Sep
      • Re: Does Null == ""?Dan Nelson16 Sep
        • Re: Does Null == ""?Bruce Feist16 Sep
          • Re: Does Null == ""?Bob Hall16 Sep
        • Re: Does Null == ""?Bob Hall16 Sep
      • RE: Does Null == ""?Jon Frisby16 Sep
        • Re: Does Null == ""?Bruce Feist16 Sep
          • RE: Does Null == ""?Jon Frisby16 Sep
            • Re: Does Null == ""?Bruce Feist16 Sep
              • RE: Does Null == ""?Jon Frisby16 Sep
              • Re: Does Null == ""?Bob Hall17 Sep
        • Re: Does Null == ""?Bob Hall16 Sep
      • Re: Does Null == ""?Bob Hall16 Sep
    • Re: Does Null == ""?Bob Hall17 Sep
      • Re: Does Null == ""?Bruce Feist18 Sep
        • Re: Does Null == ""?Bob Hall18 Sep
  • Re: Does Null == ""?Haydies18 Sep
    • Re: Does Null == ""?Bob Hall18 Sep