Add lesson 24: Arrays

[exekias]

Adds the second lesson of Module 6: Postgres power types — arrays (roadmap item 24-arrays).

What's in the lesson

• Declaring array columns and both literal forms (ARRAY[...] vs '{a,b}')
• 1-based indexing (out-of-bounds → NULL), slicing, array_length vs cardinality
• unnest (in SELECT and FROM) and array_agg
• Membership / set ops: = ANY, ALL, containment @>/<@, overlap &&
• Mutation: array_append/array_prepend/array_remove/array_cat/||/array_position
• Conversions: string_to_array/array_to_string, plus a GIN-index note (deferred to Module 7)

Seed

A 6-row articles(id, title, tags text[]) table with overlapping tags so containment/overlap/tag-cloud queries are interesting.

Checks

One query-returns check: array_append a tag to a row and verify the result.

Notes

Includes the byte-identical Module 6 module.yaml.

npm run lessons:validate and next build both pass.

Part of #6

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated (UTC)
learn-postgres	Ready	Preview	Jul 2, 2026 9:24am