OPTIONAL MATCH

Caution

The feature is still in beta. It will continue to be optimized.

The OPTIONAL MATCH clause is used to search for the pattern described in it. OPTIONAL MATCH matches patterns against your graph database, just like MATCH does. The difference is that if no matches are found, OPTIONAL MATCH will use a null for missing parts of the pattern.

OpenCypher Compatibility

This topic applies to the openCypher syntax in nGQL only.

Limitations

The WHERE clause cannot be used in an OPTIONAL MATCH clause.

Example

The example of the use of OPTIONAL MATCH in the MATCH statement is as follows:

nebula> MATCH (m)-[]->(n) WHERE id(m)=="player100" \
        OPTIONAL MATCH (n)-[]->(l) \
        RETURN id(m),id(n),id(l);
+-------------+-------------+-------------+
| id(m)       | id(n)       | id(l)       |
+-------------+-------------+-------------+
| "player100" | "team204"   | __NULL__    |
| "player100" | "player101" | "team204"   |
| "player100" | "player101" | "team215"   |
| "player100" | "player101" | "player100" |
| "player100" | "player101" | "player102" |
| "player100" | "player101" | "player125" |
| "player100" | "player125" | "team204"   |
| "player100" | "player125" | "player100" |
+-------------+-------------+-------------+

Using multiple MATCH instead of OPTIONAL MATCH returns rows that match the pattern exactly. The example is as follows:

nebula> MATCH (m)-[]->(n) WHERE id(m)=="player100" \
        MATCH (n)-[]->(l) \
        RETURN id(m),id(n),id(l);
+-------------+-------------+-------------+
| id(m)       | id(n)       | id(l)       |
+-------------+-------------+-------------+
| "player100" | "player101" | "team204"   |
| "player100" | "player101" | "team215"   |
| "player100" | "player101" | "player100" |
| "player100" | "player101" | "player102" |
| "player100" | "player101" | "player125" |
| "player100" | "player125" | "team204"   |
| "player100" | "player125" | "player100" |
+-------------+-------------+-------------+

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Last update: February 3, 2023