Redundant composite index in many-to-many docs

Open Beginner friendly

#721 opened on Sep 20, 2026 0 comments 0 reactions 0 assignees View on GitHub

Nobody has claimed this yet.

Assessment

Difficulty: 1/5
Estimated time: Under an hour
Newbie friendliness: 90/100

Issue type: Documentation
Clarity: Clearly specified
Activity status: Active
Tech stack: postgresql
Domain: databases, documentation

Research direction

Start at the linked many-to-many relationships section and review the composite primary key and index example. Update the example so it no longer includes the redundant composite index, while retaining the single-column indexes; done when the documentation matches the proposed snippet.

Written by the indexing model from the issue text.

Description

The many-to-many relations documentation recommends creating a separate composite index on (userId, groupId) in addition to a composite primary key on (userId, groupId).

In PostgreSQL (and most other DBMSs), the PK already creates a unique index covering (userId, groupId), making the additional composite index redundant.

So this:

    p.primaryKey({ columns: [t.userId, t.groupId] }),
    p.index('users_to_groups_user_id_idx').on(t.userId),
    p.index('users_to_groups_group_id_idx').on(t.groupId),
    p.index('users_to_groups_composite_idx').on(t.userId, t.groupId),      // <----- unnecessary

Should be:

    p.primaryKey({ columns: [t.userId, t.groupId] }),
    p.index('users_to_groups_user_id_idx').on(t.userId),
    p.index('users_to_groups_group_id_idx').on(t.groupId),

Dominant language: MDX
Stars: 241
Forks: 402
Avg merge: 4d 6h
Merged PRs (30d): 4

Contributor guide

No contributing guide indexed for this repository

First steps

Read the whole issue, then the project's contributing guide.
Comment on the issue to say you are picking it up — it saves two people doing the same work.
Fork the repository and make your change on a branch.
Open a pull request that references the issue number.

Similar issues

Batched `completeJobs`/`failJobs` are never retried: the retry loop in `batch()` exits after the first failure Open

Difficulty 2/5 1-3 hours Newbie friendliness 88/100

graphile/worker#636 · Opened Sep 21, 2026
Test Failure: com.ibm.ws.jdbc.fat.sqlserver.SQLServerTest J2CA0079E Open

Difficulty 2/5 1-3 hours Newbie friendliness 72/100

OpenLiberty/open-liberty#35839 · Opened Sep 21, 2026
hash join v2: 'unsupported column type for pre-alloc 225' when joining on a VECTOR column Open

affects-9.0 found-by-ai may-affects-25.10 may-affects-26.3 may-affects-26.9 may-affects-7.5 may-affects-8.1 may-affects-8.5 severity/major sig/execution type/bug

Difficulty 2/5 1-3 hours Newbie friendliness 85/100

pingcap/tidb#71473 · Opened Sep 21, 2026
JSON_VALUE fails to parse when a RETURNING clause is present but the optional ON EMPTY/ON ERROR clause is omitted Open

Difficulty 1/5 Under an hour Newbie friendliness 92/100

antlr/grammars-v4#5014 · 1 comment · Opened Sep 21, 2026
readBinary(std::vector) throws a bare Poco::Exception (POCO_EXCEPTION code 1000) for too-large sizes instead of TOO_LARGE_ARRAY_SIZE Open

comp-query-execution fuzz

Difficulty 2/5 1-3 hours Newbie friendliness 88/100

ClickHouse/ClickHouse#121303 · 3 comments · Opened Sep 21, 2026

More Databases issues