Join related rows from two tables.
Postgres: Match a category key to its display label with an explicit join condition.
CREATE TABLE lesson_items (
id INTEGER PRIMARY KEY,
name VARCHAR(40) NOT NULL,
category VARCHAR(20),
quantity INTEGER NOT NULL
);
INSERT INTO lesson_items (id, name, category, quantity) VALUES
(1, 'Tea', 'Drinks', 4),
(2, 'Coffee', 'Drinks', 8),
(3, 'Bread', 'Food', 2),
(4, 'Water', NULL, 0);
CREATE TABLE lesson_categories (code VARCHAR(20) PRIMARY KEY, label VARCHAR(40) NOT NULL);
INSERT INTO lesson_categories (code, label) VALUES ('Drinks', 'Beverages');
SELECT i.name, c.label
FROM lesson_items AS i
JOIN lesson_categories AS c ON c.code = i.category
ORDER BY i.id;Expected output EXAMPLE
Tea|Beverages Coffee|Beverages
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.
Run each example independently in an empty scratch database or schema; the example includes its own starting table and rows.
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
c22221c4e2ec77ab7f06b1f64fa7277b8093f49fe19499efa8d52deff441097a- 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
Tea|Beverages Coffee|Beverages
Exit code: 0. Standard error: empty. Validation: Exact stdout comparison. System-dependent values above are one recorded run.