Enforce uniqueness with a dedicated index.
SQL Server: A unique index rejects a duplicate combination independently of query plans.
CREATE TABLE aliases (id INTEGER PRIMARY KEY,label VARCHAR(30) NOT NULL);
CREATE UNIQUE INDEX ux_aliases_label ON aliases(label);
INSERT INTO aliases VALUES (1,'main');
SELECT label FROM aliases;Expected output EXAMPLE
main
Details
Requires SQL Server 2022 or later. Run in an empty scratch database in SSMS or sqlcmd. Result rows below use | between columns, without headers; client display formatting may differ. A unique index rejects a duplicate combination independently of query plans. 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 · · SQL Server 16.0.4295.3 · 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
4656c5248961015d792ee646405520dec7096441d271c05146a50876ce6f76ba- 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
main
Exit code: 0. Standard error: empty. Validation: Exact stdout comparison. System-dependent values above are one recorded run.
Additional assertions that passed
Checks recorded by the test harness. Where Python assertions are shown, browser cases use Playwright and simulator cases may inspect pin transitions: result.stdout is captured output, work is the temporary directory, and Path is pathlib.Path. The harness also imports json and csv.
Every tested engine rejected this invalid write with an integrity/constraint error: INSERT INTO aliases VALUES (2,'main');