Sync the supported ClickHouse functions page with mapping.py

[ivannhadz]

Changes

The Supported ClickHouse functions page describes itself as the list of "enabled ClickHouse functions" and links to mapping.py as its source of truth — but it had drifted from the engine. (posthog/hogql/functions/clickhouse/strings.py even carries the comment "Keep in sync with the posthog.com repository: contents/docs/sql/clickhouse-functions.mdx".)

This reconciles the page with the functions HogQL actually enables.

Added 17 enabled-but-undocumented functions, each in its existing section:

• Type conversions: toNullableString, toUUIDOrDefault
• Dates and times: timezone, fromUnixTimestamp64Milli, make_date, to_char, to_date, to_timestamp
• JSON: JSONExtract, JSONExtractKeysAndValues
• Conditional: throwIf
• Mathematical: rand
• Splitting strings: split_part
• Geo: geohashEncode
• Other: greatest, least, languageCodeToName

Fixed 2 errors:

• make_timestampz → make_timestamptz (typo)
• Removed JSONExtractKey — not a registered function (the engine rejects it); JSONExtractKeys is the real one and was already listed.

How this was verified

• Cross-checked the page against the function registry in posthog/hogql/functions/ (the file the page already cites as its source).
• Ran all 17 added functions in a single HogQL query against a live PostHog instance — each returned the expected result (e.g. greatest(1, 2) → 2, languageCodeToName('en') → English, split_part('a,b,c', ',', 2) → b).
• Confirmed the removed JSONExtractKey is rejected by the engine as an "Unsupported function call."

Scope is intentionally limited to clearly-missing, user-facing functions; internal UDFs (e.g. aggregate_funnel*) are excluded.

Agent context

Drafted with help from Claude (Claude Code). I've reviewed every change, understand each function, and verified them against the engine and a live instance as above.

Checklist

• I've read the docs and/or content style guides.
• Words are spelled using American English
• Use relative URLs for internal links
• I've checked the pages added or changed in the Vercel preview build
• If I moved a page, I added a redirect in vercel.json (N/A — no page moved)

[ivannhadz]

Small docs-only change: syncs the Supported ClickHouse functions page with the functions actually enabled in mapping.py (17 missing functions added, 2 errors fixed). Each added function was verified to execute against a live PostHog instance. CI is blocked on first-run workflow approval. cc @PostHog/hogql - would appreciate a look when you have a moment. 🙏