In ABAP, which JOIN is best for retrieving all records from both tables including duplicates?

The best choice for retrieving all records from both tables, including duplicates, is the FULL OUTER JOIN. This type of join combines the results of both LEFT OUTER JOIN and RIGHT OUTER JOIN, meaning it will return all records from both the left and right tables.

In a FULL OUTER JOIN, where there are matching records in both tables, those records will only appear once in the output. If a record does not have a match in the other table, it will still appear in the results, displaying null values for the columns from the non-matching table. This characteristic ensures that all records from both tables are included in the final result set, fulfilling the requirement of showing both complete datasets, even when there are duplicates.

This contrasts with other join types. A LEFT OUTER JOIN only retrieves all records from the left table, and matched records from the right table, while an INNER JOIN returns only the records with matching values from both tables. UNION, on the other hand, combines results from two SELECT statements but eliminates duplicates unless UNION ALL is used, which is not directly aimed at handling joins between two tables in the same manner as FULL OUTER JOIN.