Keep rows matching a condition.
Postgres: Use WHERE to select rows with a particular category.
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);
SELECT name FROM lesson_items WHERE category = 'Drinks' ORDER BY id;Expected output EXAMPLE
Tea Coffee
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
e5777e80e969762708be2063bbdf6e8b22a42ded2ef1aa5b1bb3f72010ba51e0- 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 Coffee
Exit code: 0. Standard error: empty. Validation: Exact stdout comparison. System-dependent values above are one recorded run.