Cypher Language Reference

MarsDB implements a subset of Cypher. It passes the full openCypher TCK. Exhaustive breakdown: CYPHER_COVERAGE.md.

Supported

• Patterns: MATCH/OPTIONAL MATCH, undirected/bracketless/multi-type/ variable-length relationship patterns, named-path capture (including over variable-length hops), shortestPath(), pattern comprehension, pattern predicates.
• Reading & filtering: WHERE (property/identity/label comparisons, pattern predicates, STARTS WITH/ENDS WITH/CONTAINS), exists { ... } (both the simple pattern form and the full nested-subquery form, including nested exists {}), UNWIND, any number of chained WITH boundaries, ORDER BY/SKIP/LIMIT, DISTINCT.
• Writing: CREATE, MERGE (with ON CREATE/ON MATCH), SET, REMOVE, DELETE/DETACH DELETE, MATCH ... CREATE, arbitrary chaining of mutating clauses via trailing WITH or RETURN. MERGE is capped at one relationship hop.
• Aggregation: implicit GROUP BY, count/sum/avg/min/max/ collect/percentileCont/percentileDisc, DISTINCT inside an aggregate call, aggregate expressions composed with arithmetic.
• Functions: the standard scalar/string/math/list function set (coalesce, toInteger/toFloat/toString/toBoolean, keys/ labels/type/properties/id, size/length/nodes/ relationships/head/tail/last/range, toUpper/toLower/ trim/replace/split/substring, abs/ceil/floor/round/ sqrt/sign).
• Temporal types: Date/LocalTime/Time/LocalDateTime/ DateTime/Duration — construction from strings, maps, or another temporal value; comparison; calendar-aware arithmetic; full component access; ISO-8601 string round-tripping.
• Stored procedures: CALL proc(args) [YIELD ...], both standalone and in-query forms, against a caller-supplied ProcedureProvider — see Embedding in Rust. MarsDB itself ships no built-in procedures.
• Parameters: $name scalars, lists (including nested lists), and maps.

Known limitations

• Node/relationship-valued $parameters aren’t supported. Scalar, list, and map parameters already work. This is on the roadmap.
• No cost-based query optimizer. Index seeks and top-k ORDER BY ... LIMIT selection exist, but join/traversal ordering isn’t cost-estimated. See Architecture. This is on the roadmap.
• CALL needs an embedder-supplied ProcedureProvider — there’s no built-in procedure catalog.

Conformance testing

Checked against the openCypher Technology Compatibility Kit (TCK) on every push: 3,880/3,880 scenarios pass across 220 feature files. Per-category numbers are in CYPHER_COVERAGE.md.

git submodule update --init marsdb-tck/openCypher
cargo run --release -p marsdb-tck