title: converting numeric to character in sqldf
body: <p>I am trying to concatenate 2 columns of a data-frame in R using sqldf command. However, it treats them as numeric and sums them up. I looked at the <a href="https://stackoverflow.com/questions/5323361/convert-numeric-value-to-varchar">solution</a>  to a similar question on stackoverflow but it still doesn't work for me. </p>
  
  <p>Here's what my DF looks like:</p>
  
  <pre><code>SP1  SP2
  521  526
  521  523
  </code></pre>
  
  <p>What I want is:</p>
  
  <pre><code>SP
  521-526
  521-523
  </code></pre>
  
  <p>I tried the following:</p>
  
  <pre><code>sqldf("select  SP1 + '-' + SP2 as SP from DF")
  </code></pre>
  
  <p>I also tried: </p>
  
  <pre><code>DF2 &lt;- transform(DF, SP1 = as.character(SP1), SP2 = as.character(SP2)))
  sqldf("select  SP1 + '-' + SP2 as SP from DF2")
  </code></pre>
  
  <p>In both cases, the result I get is </p>
  
  <pre><code>SP
  1047
  1044
  </code></pre>
  
  <p>Any thoughts?</p>