The type of join needed to include rows that do not have matching values in the other table is an Outer Join. There are three main types of outer joins:
- Left Outer Join (LEFT JOIN) : Returns all rows from the left table and the matching rows from the right table. Rows in the left table with no match in the right table will have NULLs for the right table's columns.
- Right Outer Join (RIGHT JOIN) : Returns all rows from the right table and the matching rows from the left table. Rows in the right table with no match in the left table will have NULLs for the left table's columns.
- Full Outer Join (FULL OUTER JOIN) : Returns all rows from both tables, including rows with no matching counterpart in the other table, filling with NULLs where there is no match.
For example, a FULL OUTER JOIN retrieves all records from both tables, including those without matches, with NULLs in place of missing values
. Thus, when you want to include rows without matching values, you use an Outer Join , choosing left, right, or full depending on which unmatched rows you want to include. Summary:
Join Type| Includes unmatched rows from
---|---
Left Outer Join| Left table only
Right Outer Join| Right table only
Full Outer Join| Both tables
The key is that Outer Joins preserve unmatched rows by including NULLs for missing matches, unlike inner joins which exclude them
. Therefore, the answer is: Outer Join.
