SQL Server Update query very slow
<p>I ran the following query on a previous years data and it took 3 hours, this year it took 13 days. I don't know why this is though. Any help would be much appreciated.</p>

<p>I have just tested the queries in the old SQL server and it works in 3 hours. Therefore the problem must have something to do with the new SQL server I created. Do you have any ideas what the problem might be?</p>

<p>The query:</p>

<pre><code>USE [ABCJan]
CREATE INDEX Link_Oct ON ABCJan2014 (Link_ref)
GO
CREATE INDEX Day_Oct ON ABCJan2014 (date_1)
GO

UPDATE   ABCJan2014
SET      ABCJan2014.link_id = LT.link_id
FROM     ABCJan2014 MT
INNER JOIN  [Central].[dbo].[LookUp_ABC_20142015] LT
ON MT.Link_ref = LT.Link_ref

UPDATE   ABCJan2014
SET      SumAvJT  = ABCJan2014.av_jt * ABCJan2014.n

UPDATE   ABCJan2014
SET      ABCJan2014.DayType = LT2.DayType
FROM     ABCJan2014 MT
INNER JOIN  [Central].[dbo].[ABC_20142015_days] LT2
ON  MT.date_1 = LT2.date1
</code></pre>

<p>With the following data structures:</p>

<p>ABCJan2014 (70 million rows - NO UNIQUE IDENTIFIER - Link_ref &amp; date_1 together are unique)</p>

<pre><code>Link_ID nvarchar (17)
Link_ref    int
Date_1  smalldatetime
N       int
Av_jt       int
SumAvJT decimal(38,14)
DayType nvarchar (50)
</code></pre>

<p>LookUp_ABC_20142015</p>

<pre><code>Link_ID nvarchar (17) PRIMARY KEY
Link_ref    int INDEXED
Link_metres int
</code></pre>

<p>ABC_20142015_days</p>

<pre><code>Date1   smalldatetime   PRIMARY KEY &amp; INDEXED
DayType nvarchar(50)
</code></pre>

<p>EXECUTION PLAN
<a href="https://i.stack.imgur.com/GJFAJ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GJFAJ.png" alt="enter image description here"></a></p>

<p>It appears to be this part of the query that is taking such a long time. </p>

<p>Thanks again for any help, I'm pulling my hair out.</p>