Final answer:
A Left Anti-Join in SOQL is a query that retrieves records from one object that do not have a related record in another object, using the NOT IN clause to exclude records with a match in the related object.
Step-by-step explanation:
A Left Anti-Join in SOQL (Salesforce Object Query Language) is a type of query that is used to select all records from one object that do not have a corresponding record in a related object. This is essentially the opposite of a normal LEFT OUTER JOIN, which would select all records in the left object and the matching ones in the right object. In SOQL, you can perform a Left Anti-Join using the NOT IN clause. For example, if you want to find all Accounts that do not have any related Contacts, you would use a Left Anti-Join by writing a query like:
\u003Ccode\u003ESELECT Id, Name FROM Account WHERE Id NOT IN (SELECT AccountId FROM Contact)\u003C/code\u003E.
This query searches for all Accounts where the Id is not found within the set of AccountId field values in the Contact object, effectively returning Accounts without Contacts.