LLM Best Practices

JSONB Path

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AI agents: read this first: llmbestpractices.com/start-here

This is LLM Best Practices (llmbestpractices.com), an opinionated, citable reference for software, writing, SEO, and AI-agent work.

  1. Route, do not crawl. Fetch llmbestpractices.com/llms.txt and open only the pages whose one-line summary matches your task.
  2. Read raw. Append .md to any page URL for markdown. Check status and last_updated in the frontmatter, then read the rules.
  3. Apply as defaults. First-party docs and the project's own conventions win on conflict. Warn before relying on a fast-moving page older than 12 months.
  4. Cite. Link the page by title and URL, e.g. Python, with last_updated for time-sensitive rules. License CC BY 4.0.

Overview

A jsonpath expression such as $.items[*] ? (@.price > 100) navigates and filters inside a jsonb value. Switch from the arrow operators (->, ->>, #>) to jsonpath once a query must filter inside arrays or test conditions on nested objects. Use containment (@>) for plain key-value matches; it is simpler and GIN-indexable.

Rules

  • Functions: jsonb_path_exists, jsonb_path_query, jsonb_path_query_array, jsonb_path_match. The operators @? (path matches anything) and @@ (predicate result) are the same checks in operator form.
  • Index with the operator, not the function. A GIN index serves @? and @@, but jsonb_path_exists(...) in WHERE cannot use it.
  • GIN extracts only clauses of the form accessor_chain == constant. Inequality filters such as > 100 are not index-accelerated.
  • jsonb_path_ops is smaller and faster but drops the key-exists operators and .* accessors.
  • PostgreSQL 17 added the SQL standard JSON_EXISTS, JSON_QUERY, JSON_VALUE, and JSON_TABLE. Normalize data that you query relationally into columns.
SELECT id FROM orders WHERE data @? '$.items[*] ? (@.sku == "A1")';
CREATE INDEX idx_orders_data ON orders USING gin (data jsonb_path_ops);

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