Composite queries (clause structure)¶

Composite queries put data from different queries together. They then use filters, group-bys, or sorting before returning the combined return results.

Nebula Graph supports three methods to run composite queries (or sub-queries):

• (openCypher) Clauses are chained together, and they feed intermediate result sets between each other.

• (Native nGQL) More than one query can be batched together, separated by semicolons (;). The result of the last query is returned as the result of the batch.

• (Native nGQL) Queries can be piped together by using the pipe (|). The result of the previous query can be used as the input of the next query.

OpenCypher compatibility¶

In a composite query, do not put together openCypher and native nGQL clauses in one statement. For example, this statement is undefined: MATCH ... | GO ... | YIELD ....

• If you are in the openCypher way (MATCH, RETURN, WITH, etc), do not introduce any pipe or semicolons to combine the sub-clauses.

• If you are in the native nGQL way (FETCH, GO, LOOKUP, etc), you must use pipe or semicolons to combine the sub-clauses.

Composite queries are not transactional queries (as in SQL/Cypher)¶

For example, a query is composed of three sub-queries: A B C, A | B | C or A; B; C. In that A is a read operation, B is a computation operation, and C is a write operation. If any part fails in the execution, the whole result will be undefined. There is no rollback. What is written depends on the query executor.

Examples¶

• OpenCypher compatibility statement

  # Connect multiple queries with clauses.
  nebula> MATCH p=(v:player{name:"Tim Duncan"})--() \
          WITH nodes(p) AS n \
          UNWIND n AS n1 \
          RETURN DISTINCT n1;
  

• Native nGQL (Semicolon queries)

  # Only return edges.
  nebula> SHOW TAGS; SHOW EDGES;
  
  # Insert multiple vertices.
  nebula> INSERT VERTEX player(name, age) VALUES "player100":("Tim Duncan", 42); \
          INSERT VERTEX player(name, age) VALUES "player101":("Tony Parker", 36); \
          INSERT VERTEX player(name, age) VALUES "player102":("LaMarcus Aldridge", 33);
  

• Native nGQL (Pipe queries)

  # Connect multiple queries with pipes.
  nebula> GO FROM "player100" OVER follow YIELD follow._dst AS id | \
          GO FROM $-.id OVER serve YIELD $$.team.name AS Team, \
          $^.player.name AS Player;
  +---------+-------------+
  | Team    | Player      |
  +---------+-------------+
  | Nuggets | Tony Parker |
  +---------+-------------+