本文为摘录(或转载),侵删,原文为: https://clickhouse.com/docs/en/sql-reference/data-types/lowcardinality
1 LowCardinality(T)
https://clickhouse.com/docs/en/sql-reference/data-types/lowcardinality
Changes the internal representation of other data types to be dictionary-encoded.
1.1 Syntax
1
| LowCardinality(data_type)
|
Parameters:
data_type
String
, FixedString
, Date
, DateTime
, and numbers
excepting Decimal
.- LowCardinality is not efficient for some data types, see the
allow_suspicious_low_cardinality_types
setting description.
1.2 Description
LowCardinality is a superstructure that changes a data storage method and rules of data processing. ClickHouse
applies dictionary coding to LowCardinality-columns. Operating with dictionary encoded data significantly
increases performance of SELECT queries for many applications.