Merge pull request #7567 from segmentio/DOC-1090

info note on junction table joins [DOC-1090]

Author: stayseesong

src/unify/data-graph/index.md

@@ -351,13 +351,25 @@ For many:many relationships, define the join on between the two entity tables wi
 
 **Junction table spec**
 
-| Parameters      | Definition                                                                                                                                                                                                                                                             |
-| --------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| Parameters      |Definition  |
+| --------------- | --------------------------------- |
 | `table_ref`     | Defines the fully qualified table reference to the join table: `[database name].[schema name].[table name]`. Segment flexibly supports tables, views and materialized views                                                                                             |
 | `primary_key`   | The unique identifier for the given table. Must be a column with unique values per row                                                                                                                                                                                 |
 | `left_join_on`  | Define the relationship between the left entity table and the junction table: `[left entity slug].[column name] = [junction table column name]`. Note that schema and table are implied within the junction table column name, so you do not need to define it again   |
 | `right_join_on` | Define the relationship between the junction table and the right entity table: `[junction table column name] = [right entity slug].[column name]`. Note that schema and table are implied within the junction table column name, so you do not need to define it again |
 
+
+When you define a many-to-many relationship using a junction table, `left_join_on` and `right_join_on` tell Data Graph how to connect each entity to the junction table:
+
+* Use `left_join_on` to specify which column in the junction table links to the parent (left) entity.
+
+* Use `right_join_on` to specify which column links to the child (right) entity.
+
+These fields define the join conditions, but they don’t control how the join is executed. Data Graph always performs inner joins, even if you specify a `left_join_on`.
+
+If you need behavior similar to a left join (like including unmatched rows), create a view in your warehouse with the logic you’re targeting and reference that view as an entity in your graph.
+
+
 **Example:**
 
 ```python