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ByteHouse Cloud Data Warehouse Version

System tables

system.columns

The System table system.columns contains information about all Columns, including each Column's Type, Location, key associations, compression State, and other Metadata. It can be used to view table structure details and for Analysis of Column storage characteristics.

Column name

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Name	Data type	Description
			\
database	String	The name of the Database to which the Column belongs.
			\
table	String	The name of the table to which the Column belongs.
			\
name	String	The name of the Column.
			\
type	String	The data type of the Column.
			\
position	UInt64	The Column's position in the table, starting from 1.
			\
default_kind	String	The expression type of the Column's default value. Possible values are DEFAULT, MATERIALIZED, and ALIAS. If undefined, it is an empty string.
			\
default_expression	String	The specific expression for the Column's default value. If undefined, it is an empty string.
			\
data_compressed_bytes	UInt64	The size of the Column's compressed data, in bytes.
			\
data_uncompressed_bytes	UInt64	The size of the Column's uncompressed data, in bytes.
			\
marks_bytes	UInt64	The size of the Column's mark data, in bytes.
			\
comment	String	The comment text for the Column. If not defined, it is an empty string.
			\
is_in_partition_key	UInt8	Indicates whether the Column is included in the table's partition key expression:	\
			\
		* 1 = Yes (participates in partition logic);	\
		* 0 = No.
			\
is_in_sorting_key	UInt8	Indicates whether the Column is included in the table's sorting key expression:	\
			\
		* 1 = Yes (participates in data sorting);	\
		* 0 = No.
			\
is_in_primary_key	UInt8	Indicates whether the Column is included in the table's primary key expression:	\
			\
		* 1 = Yes (used to uniquely identify data rows);	\
		* 0 = No.
			\
is_in_sampling_key	UInt8	Indicates whether the Column is included in the table's sampling key expression:	\
			\
		* 1 = Yes (participates in data sampling logic);	\
		* 0 = No.
			\
compression_codec	String	The name of the compression codec used by the Column.
			\
character_octet_length	Nullable(UInt64)	The maximum length of binary data, character data, text data, or images, in bytes. In ByteHouse, this is only valid for the `FixedString` data type; other types return `NULL`.
			\
numeric_precision	Nullable(UInt64)	The precision of approximate numeric data, exact numeric data, integer data, or currency data. In ByteHouse, it is the bit width of integer types, and the decimal precision of `Decimal` types; other types return `NULL`.
			\
numeric_precision_radix	Nullable(UInt64)	The radix of the number system, indicating the precision of approximate numeric data, exact numeric data, integer data, or currency data. In ByteHouse, integer types use 2, `Decimal` types use 10; other types return `NULL`.
			\
numeric_scale	Nullable(UInt64)	The scale of approximate numeric data, exact numeric data, integer data, or currency data. In ByteHouse, only the `Decimal` type is meaningful; other types return `NULL` values.
			\
datetime_precision	Nullable(UInt64)	The decimal precision of the `DateTime64` data type. Other data types return `NULL` values.

Example

Query column information in the sales_db.order_details table, and only retrieve key fields:

SELECT 
  name AS column_name, 
  type AS column_type, 
  is_in_primary_key, 
  is_in_partition_key, 
  default_kind 
FROM system.columns 
WHERE database = 'sales_db' 
  AND table = 'order_details' 
ORDER BY position;

Example of query results:

Last updated: 2026.03.31 16:16:45

ByteHouse Cloud Data Warehouse Version

Column name #

Example #

Column name

Example