title: Operand data type varchar is invalid for sum operator
body: <p>I try this query </p>
  
  <pre><code>Select 
  S.Name,S.No,
  SUM(Case when s.Model='Cultus' then total else 0 end) as Cultus,
  SUM(Case when s.Model ='vigo' then total else 0 end) as vigo,
  SUM(total) total_v ,
   s.MA,MAX(S.Speed) Speed
   from (
  Select
   RVU.Name,RVU.No,VV.Model,count(VV.Model) as total, RVU.MA as MA,RVU.Speed 
  from 
   VV 
  inner join RVU
  on VV.MID=RVU.ID 
  inner join RU on RVU.RID= RU.RID
      WHERE 
  RU.StartDate&gt;= '2016-04-01 00:00:00' and
  RU.EndDate&lt;='2016-04-30 23:59:59'   and
  RU.Region= 'Paris'
  and RVU.No= '651' AND Model &lt;&gt; ''
  Group By RVU.Name,RVU.RegNo,VV.Model,RVU.MA,RVU.Speed ) S
  GROUP BY
  s.RegNo,s.Name,S.MA
  </code></pre>
  
  <p>Ouput </p>
  
  <pre><code>Name    No  Cultus  vigo    total_v   MA       Speed
  David   651    2    0        2         1048      124
  David   651    3    0        3         597      345
  David   651    1    0        1         606     101
  David   651    3    2        5         992     110
  </code></pre>
  
  <p>when i try this </p>
  
  <pre><code>Sum(MA) MA,
  </code></pre>
  
  <p>THIS SHOW ERROR </p>
  
  <p><strong>Operand data type varchar is invalid for sum operator.</strong></p>
  
  <p>I want result like this </p>
  
  <pre><code>Name    No     Cultus   vigo    total_v   MA    Speed
  David   651    9         2       11       1799    345
  </code></pre>
  
  <p><strong>UPDATE</strong></p>
  
  <p>when i try this </p>
  
  <pre><code>SUM(CASE ISNULL(MA,'') WHEN '' THEN 0 ELSE CAST(MA AS INT) END),
  </code></pre>
  
  <p>and also this </p>
  
  <pre><code>sum(cast (MA as int))
  </code></pre>
  
  <p>then output is </p>
  
  <pre><code> Name   No  Cultus  vigo    total_v     MA     Speed
  David   651    2    0        2          4192     124
  David   651    3    0        3         2388      345
  David   651    1    0        1         2424      101
  David   651    3    2        5         4960      110
  </code></pre>
  
  <p><strong>updated 2:</strong></p>
  
  <p>when i execute only this part this show multiple records with same data </p>
  
  <pre><code> Select
       RVU.Name,RVU.No,VV.Model,count(VV.Model) as total, RVU.MA as MA,RVU.Speed 
      from 
       VV 
      inner join RVU
      on VV.MID=RVU.ID 
      inner join RU on RVU.RID= RU.RID
          WHERE 
      RU.StartDate&gt;= '2016-04-01 00:00:00' and
      RU.EndDate&lt;='2016-04-30 23:59:59'   and
      RU.Region= 'Paris'
      and RVU.No= '651' AND Model &lt;&gt; ''
      Group By RVU.Name,RVU.RegNo,VV.Model,RVU.MA,RVU.Speed
  </code></pre>
  
  <p>looks like value totally change</p>