Help converting SQL to C#

Hi, I have the following eSQL statements that I need to convert to C# in a console app... I'm not sure if I'm doing it correctly so any help would be greatly appreciated!

Here is the given eSQL: 

DECLARE PRODUCT_UNITS CHARACTER;
DECLARE PRODUCT_ID CHARACTER;
DECLARE output CHARACTER;

IF PRODUCT_UNITS IS NOT NULL THEN
     IF PRODUCT_UNITS > 999 THEN
           SET PRODUCT_UNITS = '999';
     END IF;
END IF;

IF ((PRODUCT_ID IS NOT NULL) AND (PRODUCT_ID <> '')) THEN
     DECLARE TEMP_PRODUCT_ID INTEGER;
     SET TEMP_PRODUCT_ID = CAST(PRODUCT_ID AS INTEGER);

      IF ((TEMP_PRODUCT_ID >= 1 ) AND (TEMP_PRODUCT_ID < 10 ) AND (LENGTH(PRODUCT_ID) < 2) ) THEN
           SET output = output || ',@X123="0' || PRODUCT_ID || ' " ';
      ELSE 
           SET output = output || ',@X123=" ' || PRODUCT_ID || ' " ';
       END IF;

END IF;

SET output;
      

Here's what I have so far:

public string Employee(string productUnits, string productId)
{
    StringBuilder output = new StringBuilder();

     if (!string.IsNullOrEmpty(productUnits))
     {
          if(int.Parse(productUnits) > 999)
          {
                 productUnits = "999";
           }
       }

  if (!string.IsNullOrEmpty(productId))
     {
          int tempProductId >= int.TryParse(productId);

          if(tempProductId >= 1 && tempProductId < 10 && int.TryParse(productId) < 2)
          {
                 output.Append(",@x123=\"0").Append(productId).Append('"');
           } 
           else
           {
                 output.Append(",@x123=\"").Append(productId).Append('"');
           }
       }

    return output.ToString();
}