Data Loader does not allow importing multiple columns into one field in Salesforce.
You can also leave unchecked cells blank if you like
Salesforce will not accept text in number fields.Remove all currency symbols and commas from the number and currency columns.Bad addresses include information like a comma instead of dot or mailto: in front of the address. Salesforce email fields will not accept bad email addresses and will cause wi bad addresses to fail. Ensure email addresses are correctly formatted.You can use Excel cell format of “Phone Number” to format phone and fax columns.Remember, you will need to do this formatting again if you convert from Excel to CSV.
Leverage the Zip Code Cell Format to put them back. If you’re working with Zip Code data that has leading zeros, Excel will remove these zeros.If not, please see the Salesforce Help Topic “ Data Loader Date Values” for other options. This assumes that you have set Data Loader settings with your local time zone. In Data Loader, fields with date values should be formatted as YYYY-MM-DD and fields with date/time values should be formatted as YYYY-MM-DD HH:MM:SS.If you apply formatting to a CSV file, save it but keep it open during the import to preserve the formatting.CSV files do not preserve formatting so if you do any data formatting in Excel and then convert to CSV, the formatting needs to be reapplied.In your Excel file prior to saving as a CSV, leverage conditional formatting functionality to highlight cells with duplicate values in columns that should not have duplicates.Ensure you have a column header and rows of data populated for all system required fields such as like Account Name or Contact Last Name.Ensure you do not have any empty columns or any columns with the same header names as this can cause field mapping issues.When finally saving as a CSV, you may want to open the file to ensure there is no corruption upon conversion, but re-save as a CSV prior to uploading to preserve date formatting. The import file must be in CSV format before you upload data however, frequently it is easier to work in Excel format to preserve formatting if you can’t finish all of your data transformation/editing in one session.Preparing your file for Salesforce Data Loader (dataloader.io): We know the Data Loader process isn’t always the most straightforward, but these tips come from our experience, and we hope they help you as much as they have helped us over the years. We’d like to share some tips with you on how you can be successful while using the Data Loader tool. Here at StarrData, we’ve helped many customers with their data management, export, transformation, and import needs.