joins

DE//AGENT currently lists 3 resources under joins: 2 tutorials, 1 skill. Everything below is derived from the live registry — counts, capabilities, verification state and security posture come from the curated records, never from marketing copy.

Documented learning objectives across these resources:

• Prove a join cannot fan out before writing it — via SQL Review
• Spot NULL-unsafe `NOT IN` and `=` predicates — via SQL Review
• State the grain of a result set in one sentence — via SQL Review
• Inspect a database with list_tables and describe_table before writing SQL — via First hands-on — a correct SELECT with a justified join
• Write a SELECT with a join whose cardinality is stated and justified — via First hands-on — a correct SELECT with a justified join

These resources map to stage: Python + SQL (3). Follow the four-phase roadmap to place this topic inside a progression instead of learning it in isolation.

Every entry, its shape and its trust state — sorted by the registry's composite score. This table is the honest version of a marketing comparison: no sponsored placements, no unverifiable claims.

How scores are computed: source quality score.

Highest composite score first:

1. SQL Review score 39.9 — beginner
2. First hands-on — a correct SELECT with a justified join score 34.15 — beginner
3. Review SQL for fan-out joins score 34.15 — beginner

Scores rank provenance, completeness and trust — read how verification works before adopting anything.

Start here if you're new: SQL Review, First hands-on — a correct SELECT with a justified join, Review SQL for fan-out joins.

Security-flagged entries: SQL Review (1 flag). Flags mean the record declares capabilities like credential use or write access — read the security posture on each page before connecting.

• SQL Review — Reviews a SQL statement for fan-out joins, NULL-unsafe predicates, implicit casts, non-deterministic ordering, and functions that silently change grain. details
• First hands-on — a correct SELECT with a justified join — Stand up a local DuckDB through the DuckDB MCP server, inspect before you query with list_tables and describe_table, and write one SELECT with a join whose cardinality you can just… details
• Review SQL for fan-out joins — Follow the SQL Reviewer agent's four-step pass over a real query: read the diff and its context, establish the grain of every result set, apply the SQL Review skill's five rules wh… details

Real install commands from the registry — read the source before running any of them:

npx de-agent-platform add sql-review

SQL Review — review first

Adjacent topics: tutorial (2 shared), review (2 shared), beginner (2 shared), correctness (2 shared).

Study path: the roadmap places this topic in a progression · the scoring model explains the numbers · the trust rule catalog shows every security check these entries passed through.