v.18.12Experimental Feature
Added LowCardinality Data Type for Efficient Data Processing
Added the LowCardinality(T) data type. This data type automatically creates a local dictionary of values and allows data processing without unpacking the dictionary. #2830Why it matters
TheLowCardinality(T) data type is designed to improve performance and reduce memory usage when working with columns containing many repeated values by storing them as dictionary-encoded data. This minimizes the overhead of handling repeated data and accelerates query execution.How to use it
To use this feature, define table columns with theLowCardinality(T) type, where T is the underlying data type, for example: LowCardinality(String). ClickHouse will automatically manage the local dictionary and optimize queries accordingly.