[b41sh]

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Summary

• Allow creating a materialized view in a different database from its source table, e.g. CREATE MATERIALIZED VIEW db2.mv AS SELECT c1 FROM db1.t WHERE 1 = 1. The source still has to be in the same catalog as the MV.
• Query rewrite: when looking up an MV's database, use mget_database_names_by_ids instead of get_db_name_by_id. A dropped database keeps its id-to-name mapping until GC, and get_db_name_by_id still returns that name. Before this change, dropping the MV's database made every query on the source table fail with UnknownDatabase. MVs in a dropped database are now skipped, the same as dropped MVs.
• system.materialized_views: list_materialized_views_impl now reads the source database's DatabaseMeta in the same MGET. An MV whose source database is dropped is reported as invalid = 1 instead of 0.
• Tests: 05_0017_ddl_materialized_view.test covers creating a cross-database MV, refreshing it, reading it, the invalid state after DROP DATABASE and UNDROP DATABASE on the source database, and querying the source after the MV's database is dropped.

fixes: #[Link the issue here]

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

AI assistance

• AI usage: An AI coding agent drafted the binder and meta changes and the logic test updates
• Responsible human: @b41sh
• The responsible human has read every line of this diff and can explain each change

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This change is 

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-30T13:09:12.228574Z	dbe8814	PR opened

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⏱ CI timing · Dev

run 41074104023 · attempt 2 (wall time includes re-run gap) · 53.0 min (main p50 63.3 min, −10.3 min)

stage	this run	main p50	Δ
total	53.0 min	63.3 min	−10.3 min
build (aarch64, ci profile)	21.0 min	23.4 min	−2.4 min
├ deps + crates (parallel)	4.1 min	—	—
├ databend-query codegen	2.9 min	—	—
├ databend-binaries link	11.9 min	—	—
└ sccache hit rate	98.5 %	—	—
test_unit	18.1 min	17.6 min	+0.5 min
mac_check	—	13.1 min	—
tests after build (49 jobs)	29.6 min	30.4 min	−0.8 min
├ queue p50 / max	3.9 min / 20.8 min	4.9 min / 26.9 min	−1.1 min
├ sqllogic standalone (8 jobs, max)	4.4 min	4.3 min	+0.1 min
├ sqllogic cluster (8 jobs, max)	7.9 min	7.2 min	+0.7 min
├ sqllogic stage (2 jobs, max)	6.5 min	5.0 min	+1.5 min
├ sqllogic other (10 jobs, max)	5.9 min	5.7 min	+0.2 min
├ stateless (2 jobs, max)	7.1 min	6.7 min	+0.4 min
├ stateful (4 jobs, max)	5.1 min	4.8 min	+0.4 min
├ compat (6 jobs, max)	6.4 min	5.7 min	+0.8 min
├ meta / logs / lineage / udf (5 jobs, max)	4.6 min	4.4 min	+0.1 min
├ ee (2 jobs, max)	1.6 min	1.3 min	+0.3 min
├ private_tasks (1 jobs, max)	8.8 min	8.8 min	−0.0 min
└ fuzz (1 jobs, max)	1.3 min	1.1 min	+0.2 min

_{Minutes unless stated; durations exclude queue time unless stated; "max" = longest job in the group. Baseline = median of the last 10 successful runs (Dev: Main on main; Cloud: recent Cloud runs). Build breakdown has no baseline. Updated on each push.}