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UPDATE query not working...


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I'm trying to change all school served email addresses to NULL because they are mostly static and in the schools data table.  Some coaches list their non-school email address, so I keep that with them as they change jobs.  I'm mostly just trying to clean up the coach data table to make sure I don't have conflicting information.  However, the below query is changing all the rows to NULL, including the ones with gmail and yahoo.  

update a_coach set server = NULL
where server != "gmail.com" or server != "yahoo.com"

I've also tried it with <> instead of !=.  Same result. This seems like it should've been pretty straight forward.  

image.thumb.png.12e9ed0b7cb9adaffe46b453550518a5.png

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Simple boolean algebra

NOT (A OR B) = NOT A AND NOT B

As you have it,

  • if the server=yahoo then it is not equal to gmail - so that condition is satisfied and therefore set to NULL
  • if the server=gmail then it is not equal to yahoo- so that condition is satisfied and therefore set to NULL
Edited by Barand
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