title: update an SQL table via R sqlSave
body: <p>I have a data frame in R having 3 columns, using sqlSave I can easily create a table in an SQL database:</p>
  
  <pre><code>channel &lt;- odbcConnect("JWPMICOMP")
  sqlSave(channel, dbdata, tablename = "ManagerNav", rownames = FALSE, append = TRUE, varTypes = c(DateNav = "datetime"))
  odbcClose(channel)
  </code></pre>
  
  <p>This data frame contains information about Managers (Name, Nav and Date) which are updatede every day with new values for the current date and maybe old values could be updated too in case of errors.</p>
  
  <p>How can I accomplish this task in R? </p>
  
  <p>I treid to use sqlUpdate but it returns me the following error:</p>
  
  <pre><code>&gt; sqlUpdate(channel, dbdata, tablename = "ManagerNav")
  Error in sqlUpdate(channel, dbdata, tablename = "ManagerNav") : 
    cannot update ‘ManagerNav’ without unique column
  </code></pre>