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Add warning about easily breaking replication

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Stig Bakken 2021-12-13 11:35:41 +01:00
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docs/en/engines/database-engines/materialized-mysql.md
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@ -194,6 +194,14 @@ when the `CREATE DATABASE` query executes, so extra care needs to be taken.
You may specify overrides for tables that do not exist yet.
!!! note "Warning"
It is easy to break replication with TABLE OVERRIDEs if not used with care. For example:
* If a column is added with a table override, but then later added to the source MySQL table, the converted ALTER TABLE
query in ClickHouse will fail because the column already exists.
* It is currently possible to add overrides that reference nullable columns where not-nullable are required, such as in
`ORDER BY` or `PARTITION BY`.
## Examples of Use {#examples-of-use}
Queries in MySQL: