Memgraph ZeroMemGQLConnectto PostgreSQL

PostgreSQL

The PostgreSQL connector (CONNECTOR_TYPE=postgres) translates GQL queries into SQL and executes them against PostgreSQL. It requires a mapping file that maps graph patterns to relational tables.

1. Start PostgreSQL

docker network create memgql-net
 
docker run -d --rm \
    --name postgres-dev \
    --network memgql-net \
    -p 5432:5432 \
    --env POSTGRES_PASSWORD=postgres \
    postgres:18

2. Seed data

docker exec -i postgres-dev psql -U postgres << 'SQL'
CREATE TABLE IF NOT EXISTS persons (
    id SERIAL PRIMARY KEY,
    name TEXT NOT NULL,
    age INT
);
CREATE TABLE IF NOT EXISTS companies (
    id SERIAL PRIMARY KEY,
    name TEXT NOT NULL
);
CREATE TABLE IF NOT EXISTS knows (
    from_id INT REFERENCES persons(id),
    to_id INT REFERENCES persons(id)
);
CREATE TABLE IF NOT EXISTS works_at (
    person_id INT REFERENCES persons(id),
    company_id INT REFERENCES companies(id)
);
 
INSERT INTO persons (id, name, age) VALUES (1, 'Alice', 30), (2, 'Bob', 25);
INSERT INTO companies (id, name) VALUES (1, 'Acme Corp');
INSERT INTO knows (from_id, to_id) VALUES (1, 2);
INSERT INTO works_at (person_id, company_id) VALUES (1, 1);
SQL

3. Start MemGQL

docker run --rm \
    --name memgql \
    --network memgql-net \
    --stop-timeout 2 \
    -p 7688:7688 \
    --env CONNECTOR_TYPE=postgres \
    --env POSTGRES_URL="host=postgres-dev user=postgres password=postgres dbname=postgres" \
    --env MAPPING_FILE=/data/mapping.json \
    --env BOLT_LISTEN_ADDR=0.0.0.0:7688 \
    -v ./mapping.json:/data/mapping.json \
    memgraph/memgql:latest

4. Connect

mgconsole --port 7688

5. Query

MATCH (p:Person) RETURN p.name, p.age;
MATCH (p:Person)-[:WORKS_AT]->(c:Company) RETURN p.name, c.name;
MATCH (a:Person)-[:KNOWS]->(b:Person) RETURN a.name, b.name;

For environment variables, see Reference.

Supported GQL features

FeaturePostgres
MATCH / WHERE / RETURN✓
Pattern-level WHERE (MATCH (n WHERE …))✓
Multiple MATCH clauses in one query✓
OPTIONAL MATCH✓
WITH clause (chain query steps)✓
WITH DISTINCT / WITH … ORDER BY … LIMIT N✓
Multiple chained WITH steps✓
Pass a whole node through WITH n✓
Typed edge (a)-[r:R]->(b)✓
Untyped edge ()-[]->(b)✗
UNION / UNION ALL / UNION DISTINCT✓
Quantified path (){m,n} — bounded✓
Map projections RETURN n {.a, .b}✓
IN list membership WHERE x IN [...]✓
STARTS WITH / ENDS WITH / CONTAINS✓
collect() aggregate✓
count, sum, avg, min, max✓
COUNT(DISTINCT …)✓
Arithmetic + - * / %✓
CASE WHEN … THEN … ELSE … END✓
COALESCE, NULLIF✓
INSERT (a {…}) RETURN a.x✓
DELETE✓
SET / REMOVE (property update / delete)✗
DETACH DELETE✗
INTERSECT / EXCEPT✗
Quantified path (){m,} — unbounded✗
Shortest-path (ALL SHORTEST / SHORTEST k)✗

Known limitations

  • Unbounded variable-length paths (()-[*]->()) are rejected. Bound the depth ({1,5}) or run the query against a Cypher backend.
  • FOR x IN [...] (UNWIND-style) is rejected with an actionable error. Cypher backends (Memgraph, Neo4j) handle this syntax natively.
  • Path variables on variable-length patterns — MATCH p = (a){1,3}(b) RETURN p is not supported. Drop the p = binding (or query a Cypher backend) and RETURN the individual nodes / edges instead.
  • RETURN n returns the node’s column values rather than a single structured node object. For a structured result, use a map projection: RETURN n {.id, .name} AS info.
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