Database

We will use the database, whose schema and data import commands are given here:

You can import this database by copy pasting the commands on that page.

UNION

UNION is the clause where you combine query result A and query result B that have the same schema but were produced by different queries into a single result C by taking their union. Two notes:

• The number of columns and dataType of each column must be identical in A and B but their names can be different.
• UNION will remove all duplicates in the union of A and B. Instead, UNION ALL preserves the duplicates.

For example, the following query returns the age of the follower of Zhang and Karissa without duplicate elimination

Query:

MATCH (u1:User)-[:Follows]->(u2:User)
WHERE u2.name = 'Zhang'
RETURN u1.age
UNION ALL
MATCH (u3:User)-[:Follows]->(u4:User)
WHERE u4.name = 'Karissa'
RETURN u3.age;

Result:

----------
| u1.age |
----------
| 30     |
----------
| 40     |
----------
| 30     |
----------

View example in Colab.

If you changed UNION ALL to UNION in the above query, one of the 30’s in the output would be removed. So the result would be:

------
| 30 |
------
| 40 |
------