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From: Tyler Hobbs <tyler@datastax.com>
Date: Tue, 6 May 2014 18:19:06 -0500
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 <CAAam9stkC6rKQ3bMNE01Mv0usuqDgaFKU0uOZJ6673BNBm0BoQ@mail.gmail.com>
Subject: Re: Avoiding email duplicates when registering users
To: user@cassandra.apache.org
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On Mon, May 5, 2014 at 10:27 AM, Ignacio Martin <natx.mc@gmail.com> wrote:

>
> When a user registers, the server generates a UUID and performs an INSERT
> ... IF NOT EXISTS into the email_to_UUID table. Immediately after, perform
> a SELECT from the same table and see if the read UUID is the same that the
> one we just generated. If it is, we are allowed to INSERT the data in the
> user table, knowing that no other will be doing it.
>

INSERT ... IF NOT EXISTS is the correct thing to do here, but you don't
need to SELECT afterwards.  If the row does exist, the query results will
show that the insert was not applied and the existing row will be returned.


-- 
Tyler Hobbs
DataStax <http://datastax.com/>

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<div dir=3D"ltr"><div class=3D"gmail_extra"><br><div class=3D"gmail_quote">=
On Mon, May 5, 2014 at 10:27 AM, Ignacio Martin <span dir=3D"ltr">&lt;<a hr=
ef=3D"mailto:natx.mc@gmail.com" target=3D"_blank">natx.mc@gmail.com</a>&gt;=
</span> wrote:<br>

<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex"><div><br></div><div>When a user registers, t=
he server generates a UUID and performs an INSERT ... IF NOT EXISTS into th=
e email_to_UUID table. Immediately after, perform a SELECT from the same ta=
ble and see if the read UUID is the same that the one we just generated. If=
 it is, we are allowed to INSERT the data in the user table, knowing that n=
o other will be doing it.</div>


<div></div></blockquote></div><br>INSERT ... IF NOT EXISTS is the correct t=
hing to do here, but you don&#39;t need to SELECT afterwards.=C2=A0 If the =
row does exist, the query results will show that the insert was not applied=
 and the existing row will be returned.<br>

<br clear=3D"all"><br>-- <br><font color=3D"#888888">Tyler Hobbs<span></spa=
n><br>
<a href=3D"http://datastax.com/" target=3D"_blank">DataStax</a><br></font>
</div></div>

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