Union and join basics in Tableau - Cell-by-Cell Formula Trace

Sample Data

Two tables for union (left and right) with customer info, and one table for join with sales data.

Cell	Value
A1	ID
B1	Name
C1	City
A2	1
B2	Alice
C2	New York
A3	2
B3	Bob
C3	Chicago
A4	3
B4	Charlie
C4	Seattle
E1	ID
F1	Name
G1	City
E2	4
F2	Diana
G2	Boston
E3	5
F3	Evan
G3	Denver
E4	6
F4	Fiona
G4	Austin
I1	ID
J1	Name
K1	City
L1	Sales
I2	1
J2	Alice
K2	New York
L2	100
I3	2
J3	Bob
K3	Chicago
L3	150
I4	7
J4	George
K4	Miami
L4	200

Formula Trace

UNION(Table1, Table2) and LEFT JOIN UNION(Table1, Table2) with SalesTable on ID

Step 1: UNION(Table1, Table2)

Step 2: LEFT JOIN (Result of UNION) with SalesTable on ID

Cell Reference Map

  A      B       C       E      F       G       I      J       K       L
+-----+-------+-------+-----+-------+-------+-----+-------+-------+-------+
| ID  | Name  | City  | ID  | Name  | City  | ID  | Name  | City  | Sales |
|  1  | Alice | New York |  4  | Diana | Boston|  1  | Alice | New York |  100  |
|  2  | Bob   | Chicago |  5  | Evan  | Denver|  2  | Bob   | Chicago |  150  |
|  3  | Charlie| Seattle | 6  | Fiona | Austin|  7  | George| Miami |  200  |
+-----+-------+-------+-----+-------+-------+-----+-------+-------+-------+
  ^       ^       ^       ^       ^       ^       ^       ^       ^       ^
  |       |       |       |       |       |       |       |       |       |
  +-------+-------+-------+-------+-------+-------+-------+-------+-------+
References: Table1 (A1:C4), Table2 (E1:G4), SalesTable (I1:L4)

Shows the three tables with their columns and rows. Arrows indicate these cells are referenced in union and join operations.

Result

  M      N       O       P
+-----+-------+-------+-------+
| ID  | Name  | City  | Sales |
|  1  | Alice | New York |  100  |
|  2  | Bob   | Chicago | 150  |
|  3  | Charlie | Seattle | null |
|  4  | Diana | Boston | null  |
|  5  | Evan  | Denver | null  |
|  6  | Fiona | Austin | null  |
+-----+-------+-------+-------+

Final table after union and left join. All customers from both tables appear with sales data where available; missing sales show null.

Sheet Trace Quiz - 3 Questions

What does the UNION operation do with the two tables?

A Stacks all rows from both tables vertically, keeping all columns

B Matches rows by ID and combines columns side by side

C Keeps only rows that appear in both tables

D Removes duplicate rows and columns

Key Result

UNION stacks rows vertically from two tables; LEFT JOIN adds columns from another table matching on key, keeping all left rows.