Accessible in: Salesforce Classic (not accessible in all organizations) and Lightning Experience
Accessible in: All Editions, with the exception of Database.com
Organization import not accessible in: Personal Edition, Database.com
The Data Import Wizard permits you to coordinate records in various manners to forestall copies. You can coordinate contacts by Salesforce ID, name, email, or outside ID. You can coordinate business accounts by Salesforce ID, outside ID, or by name and site. Coordinating by Salesforce ID is comprehensive of the two contacts and business accounts. On the off chance that you coordinate one by Salesforce ID, the other is likewise coordinated by Salesforce ID.
Don't forget to check out: Download Notes & Attachments from Force.com Site of Lightning Component
Coordinating by Name and Site
In the event that you are coordinating contacts by name and business accounts by name and site (which are the suggested alternatives), the Data Import Wizard makes a business represent every one of a kind business account name and site in the import document. It additionally makes a different contact for each contact name recorded in the document. The contacts are then connected with suitable business accounts.
In the event that the business record or contact exists in the framework, and you have perused/put down access to the account, the wizard adds your import information to the current information in Salesforce.
Coordinating by Salesforce ID
You can likewise decide to coordinate contacts and business accounts by Salesforce ID. With this choice, the Salesforce ID is the model for de-duplication. That is, on the off chance that you are coordinating by ID and a record in your source document has a similar ID as a record in Salesforce, that record is refreshed in Salesforce. Record IDs are case-delicate and must match precisely.
Coordinating by External ID
An outer ID is a custom field that has the External ID trait, implying that it contains one of a kind record identifiers from a framework outside of Salesforce. At the point when you select this choice, the Data Import Wizard recognizes existing records in Salesforce with outer IDs that coordinate those qualities in the import document.
This activity isn't a case-delicate. For instance, "ABC" is coordinated with "abc". Be that as it may, if the outside ID field additionally has the case-touchy Unique quality, coordinating by outer ID doesn't consider capitalized and lowercase letters indistinguishable.
Outside IDs can be of type text, number, email, or auto-number. On the off chance that the outside ID type is auto-number, it isn't accessible for coordinating, however, you can go through it to look the parent record in the event that it contains the outer ID.
Normalize External ID esteems before playing out the import to forestall unintended matches.
Different records with a similar External ID inside a document aren't transferred.
Different outside ID fields can discover coordinating records in Salesforce when you utilize the Data Import Wizard.
Just one of a kind External ID fields are accessible to coordinate by.
Check out another amazing blog by Mohit here: An Introduction to Salesforce Force.com Migration Tool (ANT)
Overwriting Existing Account Values
The wizard never overwrites your current business account fields except if you select Overwrite existing record esteems. This choice allows you to embed or refresh existing business account fields with new information. In any case, you can't utilize this choice to refresh existing field information with clear qualities. On the off chance that you don't choose this alternative, the wizard refreshes the unfilled business account fields, yet doesn't contact fields with information.
In the event that you don't have perused/compose access to a current business record or contact, the wizards make another business record or contact claimed by you. Likewise, the wizards make new business records and contacts dependent on explicit fields in your import document.
In Professional, Enterprise, Unlimited, Performance, and Developer Edition organizations, the import wizards can likewise import new business record and contact notes. The wizards don't import takes note of that are careful copies of existing contact or business account notes.
To import records or contact notes, make the proprietor field in the imported document the Salesforce ID.