- A join allows for combining two datasets based on matching field (referred to as a "Join Clause" in Tableau Prep)
- In the examples below we are using ID as the "Join Clause"
- Depending on the type of join used your resulting dataset will vary
- For instance, an inner join will only include IDs found in both databases (so, the inside of the Venn Diagram). A left join will add all values in the first database and those of the second that have matching ID values
- If no value is found the empty cell will be represented as Null
Original Datasets
Database A | | Database B |
ID | Fruit | | ID | Vegetable |
1 | Apple | | 3 | Lettuce |
2 | Pear | | 4 | Carrot |
3 | Orange | | 5 | Celery |
4 | Lemon | | 6 | Broccoli |
The four main types of joins, and their resulting output datasets, are shown below.
Inner Join 
| Database Join | | ID | Fruit | Vegetable |
|---|
| 3 | Orange | Lettuce | | 4 | Lemon | Carrot |
| Left Join 
| Database Join | | ID | Fruit | Vegetable |
|---|
1 | Apple | Null | 2 | Pear | Null | | 3 | Orange | Lettuce | | 4 | Lemon | Carrot |
|
| Right Join 
| Database Join | | ID | Fruit | Vegetable |
|---|
| 3 | Orange | Lettuce | | 4 | Lemon | Carrot | 5 | Null | Celery | | 6 | Null | Broccoli |
| Full Join 
| Database Join | | ID | Fruit | Vegetable |
|---|
1 | Apple | Null | 2 | Pear | Null | | 3 | Orange | Lettuce | | 4 | Lemon | Carrot | 5 | Null | Celery | | 6 | Null | Broccoli |
|