title: Incorrect parameter count in the call to native function 'ISNULL'
body: <p>I have a query that I am trying to convert to MySQL from MS SQL Server 2008. It runs fine on MSSQL,
  I get the error 
  "<code>Incorrect parameter count in the call to native function 'ISNULL'</code>". </p>
  
  <p>How do I solve this?</p>
  
  <pre><code>SELECT DISTINCT
      dbo.`@EIM_PROCESS_DATA`.U_Tax_year,
      dbo.`@EIM_PROCESS_DATA`.U_Employee_ID,
      CASE
          WHEN dbo.`@EIM_PROCESS_DATA`.U_PD_code = 'SYS033' THEN SUM(dbo.`@EIM_PROCESS_DATA`.U_Amount)
      END AS PAYE,
      CASE
          WHEN dbo.`@EIM_PROCESS_DATA`.U_PD_code = 'SYS014' THEN SUM(dbo.`@EIM_PROCESS_DATA`.U_Amount)
      END AS TOTALTAXABLE,
      dbo.OADM.CompnyName,
      dbo.OADM.CompnyAddr,
      dbo.OADM.TaxIdNum,
      dbo.OHEM.lastName + ', ' + ISNULL(dbo.OHEM.middleName, '') + '' + ISNULL(dbo.OHEM.firstName, '') AS EmployeeName
  FROM
      dbo.`@EIM_PROCESS_DATA`
          INNER JOIN
      dbo.OHEM ON dbo.`@EIM_PROCESS_DATA`.U_Employee_ID = dbo.OHEM.empID
          CROSS JOIN
      dbo.OADM
  GROUP BY dbo.`@EIM_PROCESS_DATA`.U_Tax_year , dbo.`@EIM_PROCESS_DATA`.U_Employee_ID , dbo.OADM.CompnyName , dbo.OADM.CompnyAddr , dbo.OADM.TaxIdNum , dbo.OHEM.lastName , dbo.OHEM.firstName , dbo.OHEM.middleName , dbo.`@EIM_PROCESS_DATA`.U_PD_code
  </code></pre>
  
  <p>MySQL</p>
  
  <pre><code>SELECT DISTINCT 
       processdata.taxYear, processdata.empID, 
       CASE WHEN processdata.edCode = 'SYS033' THEN SUM (processdata.amount) END AS PAYE, 
       CASE WHEN processdata.edCode = 'SYS014' THEN SUM (processdata.amount) END AS TOTALTAXABLE, 
       company.companyName, company.streetAddress, company.companyPIN, employeemaster.lastName + ', ' + IFNULL(employeemaster.middleName, '') 
       + ' ' + IFNULL(employeemaster.firstName, '') AS EmployeeName
  FROM         
       processdata INNER JOIN
       employeemaster ON processdata.empID = employeemaster.empID 
       CROSS JOIN company
       GROUP BY processdata.taxYear, processdata.empID, company.companyName, company.streetAddress, company.companyPIN, 
       employeemaster.lastName, employeemaster.firstName, employeemaster.middleName, processdata.edCode
  </code></pre>