Copy FROM subquery

You can bulk import the results of a subquery like MATCH .... by attaching that query as a subquery of a COPY FROM statement. This is useful when you need to transform data before inserting it into the database, or if you want to copy data from a LOAD FROM scan operation on a data structure that’s already in memory, such as Pandas DataFrames.

For example, consider that we have a graph with a User node label and a Follows relationship type. We want to create a new Person node table and a Knows relationship table, where we state that a Person knows another Person if they follow each other. We can use the COPY FROM command with a subquery to achieve this as follows:

Create node/relationship tables

CREATE NODE TABLE Person(name STRING, PRIMARY KEY (name));
CREATE REL TABLE Knows(FROM Person TO Person);

COPY FROM a MATCH subquery

COPY Person FROM (MATCH (a:User) RETURN a.name);
COPY Knows FROM (MATCH (a:User)-[r:Follows]->(b:User) RETURN a.name, b.name);

COPY FROM a Pandas DataFrame

An alternate use case for this feature would be when you want to directly scan data from an existing object, such as a Pandas DataFrame using LOAD FROM and use its results as input to the COPY FROM command. This can be combined with predicate filters as follows:

# First, ensure you create a Kùzu connection object and define a node table as follows:
# conn.execute("CREATE NODE TABLE Person (name STRING, age INT64, PRIMARY KEY(name))")
import pandas as pd

df = pd.DataFrame({
    "name": ["Adam", "Karissa", "Zhang", "Noura"],
    "age": [30, 40, 50, 25]
})

conn.execute("COPY Person FROM (LOAD FROM df WHERE age < 30 RETURN *)")

Using COPY FROM with subqueries in this manner opens up a wider range of possibilities for data manipulation and transformation prior to doing bulk-insertion into Kùzu.