fix: MySQL introspection failing on MariaDB servers

[sorenbs]

Fixes #1367, fixes #1511

Root cause

The tables-introspection query aggregates column metadata with cast(coalesce(json_arrayagg(json_object(...)), '[]') as json). This breaks on MariaDB two ways:

• MariaDB < 10.5 has no json_arrayagg at all (prisma studio error: FUNCTION pomagamy.json_arrayagg does not exist #1511, FUNCTION json_arrayagg does not exist)
• MariaDB has no JSON cast type (JSON is a LONGTEXT alias), so cast(... as json) is a syntax error on every version (Support MariaDB. #1367)

Fix

• The adapter detects the server flavor once per instance via select version() (matches MariaDB case-insensitively, incl. 5.5.5-…-MariaDB prefixed strings; detection failure falls back to the MySQL SQL).
• On MariaDB, aggregation uses coalesce(concat('[', group_concat(json_object(...) separator ','), ']'), '[]') — valid on all supported MariaDB versions.
• New normalizeTablesQueryResult() parses string columns payloads for all flavors (transport-agnostic; equivalent to the JS-side hardening proposed in fix mysql introspection json columns #1495, which this supersedes at the SQL level).

Verification

• End-to-end against real MariaDB 10.4 and 10.11 Docker containers: introspection succeeds with correct tables, PKs, autoincrement, enum options, FKs, generated columns, and timezone.
• pnpm test:data:mysql against local Vitess/MySQL: 38/38 pass — the MySQL SQL path is byte-identical (snapshot-asserted).
• 18 new unit tests (flavor detection, SQL branching, string-payload parsing, caching); typecheck/lint clean; changeset included.

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 3230a369-fe24-4917-85f6-071a0c274438

📥 Commits

Reviewing files that changed from the base of the PR and between 6f30bcc and 9eccabc.

📒 Files selected for processing (5)

• .changeset/mariadb-introspection-compat.md
• FEATURES.md
• data/mysql-core/adapter.ts
• data/mysql-core/introspection.mariadb.test.ts
• data/mysql-core/introspection.ts

Walkthrough

The MySQL adapter now queries select version() to detect MariaDB, caches the detected flavor, and uses MariaDB-compatible group_concat(json_object(...)) aggregation when needed. MySQL continues using json_arrayagg. Introspection results now parse stringified column payloads and validate their shape. New tests cover query generation, detection, fallback, caching, normalization, and end-to-end adapter behavior. Documentation and a patch changeset describe the compatibility update.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: fixing MariaDB introspection in the MySQL adapter.
Description check	✅ Passed	The description is directly about the MariaDB introspection fix and matches the changeset.
Linked Issues check	✅ Passed	The changes address both linked issues by supporting MariaDB and avoiding unsupported JSON_ARRAYAGG/CAST syntax.
Out of Scope Changes check	✅ Passed	The diff stays focused on MariaDB introspection, tests, and docs with no obvious unrelated additions.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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👉 Steps to fix this

Actionable comments posted: 1

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Verify each finding against current code. Fix only still-valid issues, skip the
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Inline comments:
In `@data/mysql-core/introspection.ts`:
- Around line 172-179: The MariaDB branch in the aggregated query must not use
group_concat, because group_concat_max_len can truncate column metadata. Replace
this aggregation with a non-truncating path that returns one row per column and
groups results client-side, or an equivalent approach independent of the session
cap, while preserving normalizeTablesQueryResult behavior. Add a regression test
covering a metadata payload larger than the default 1 MB limit.

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Fix all unresolved CodeRabbit comments on this PR:

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 0496bcf5-f900-4973-a8e5-4c087ef75d75

📥 Commits

Reviewing files that changed from the base of the PR and between 81354ff and 6f30bcc.

📒 Files selected for processing (5)

• .changeset/mariadb-introspection-compat.md
• FEATURES.md
• data/mysql-core/adapter.ts
• data/mysql-core/introspection.mariadb.test.ts
• data/mysql-core/introspection.ts