Find parents with at least two child rows.
Postgres: Use a correlated count when testing a per-parent threshold.
CREATE TABLE people (id INTEGER PRIMARY KEY, name VARCHAR(30));
CREATE TABLE orders (id INTEGER PRIMARY KEY, person_id INTEGER, amount INTEGER);
INSERT INTO people VALUES (1,'Ada'),(2,'Grace'),(3,'Lin');
INSERT INTO orders VALUES (1,1,10),(2,1,20),(3,2,5);
SELECT p.name FROM people p WHERE (SELECT COUNT(*) FROM orders o WHERE o.person_id=p.id)>=2 ORDER BY p.id;Expected output EXAMPLE
Ada
Details
Requires PostgreSQL 18. Run in an empty scratch schema using psql or a SQL client. Result rows below use | between columns, without headers; client display formatting may differ. Use a correlated count when testing a per-parent threshold. The CREATE and INSERT statements provide all input data. Run the complete example in a fresh scratch database or schema.
Tested on Ubuntu 24.04.5 LTS · · PostgreSQL 18.6 (Debian 18.6-1.pgdg13+2) · bash 5.2.21-2ubuntu4; coreutils 9.4-3ubuntu6.3; psycopg 3.2.10; pymssql 2.3.8
Test inputs, results and environment
The exact published code ran in a dedicated Linux test container with prepared inputs. Snippet process uid 65534 with a read-only root filesystem and temporary working files. Database services use a private internal Docker network without published ports. Fresh scratch schema/database for each case; test database administrator credentials are confined to these disposable services. Fixtures and output records are isolated from the application database. Testing covers this example and its stated checks, not every input, operating system, or runtime version. The Linux container shares its host's kernel; this is not a native Windows test.
- Architecture / host kernel
- x86_64 / 6.18.54.1-microsoft-standard-WSL2
- Snippet identity / locale
- uid=65534, gid=65534 (unprivileged process) / C.UTF-8
- Interpreter invocation
Execute the exact SQL in a fresh database/schema; serialize result rows with | separators- Container image ID
sha256:ec91410a8f6ec3e985830b5e3a0560306d36f8c1c5ccd91a6699abe707123fa3- Code SHA-256
7cc7ff8393252880d9ab0ae168fd2d8e8c288cec00587514ab701a037a1bc6b9- Dependencies
- bash 5.2.21-2ubuntu4; coreutils 9.4-3ubuntu6.3; psycopg 3.2.10; pymssql 2.3.8
Test input setup
These are the prepared inputs used by the test harness. See Details above for the prerequisites and how to run this example.
# No input files required.
Observed standard output
Ada
Exit code: 0. Standard error: empty. Validation: Exact stdout comparison. System-dependent values above are one recorded run.