v.20.4Improvement

Function toString is Monotonic for Index Analysis in Tautological Cases

Official CH changelog text
The function toString is considered monotonic and can be used for index analysis even when applied in tautological cases with String or LowCardinality(String) argument. #10110 (Amos Bird)
The toString function is now recognized as monotonic for index analysis when used with String or LowCardinality(String) arguments.

Why it matters

This improvement allows more accurate index utilization in query optimization by treating toString as a monotonic function, even in tautological cases, enhancing query performance with String types.

How to use it

Users can benefit from this feature automatically when using toString on String or LowCardinality(String) columns in queries, as the query planner will consider it monotonic during index analysis without requiring any special configuration.

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