Module column 

Column type implementations for all ClickHouse data types.

Column Module

This module provides implementations for all ClickHouse column types used in the native TCP protocol.

ClickHouse Documentation

• Data Types Overview
• Nullable Type
• Array Type
• LowCardinality Type
• Tuple Type
• Map Type

Type Nesting Restrictions

ClickHouse enforces strict rules about type nesting. The following combinations are NOT allowed:

Invalid Nesting	Error	Workaround
Nullable(Array(...))	“Nested type Array(…) cannot be inside Nullable type” (Error 43)	Use Array(Nullable(...))
Nullable(LowCardinality(...))	“Nested type LowCardinality(…) cannot be inside Nullable type”	Use LowCardinality(Nullable(...))
Nullable(Array(LowCardinality(...)))	Same as above	Use Array(LowCardinality(Nullable(...))) or Array(Nullable(LowCardinality(...)))

Correct Nesting Order:

• ✅ Array(Nullable(T)) - Array of nullable elements
• ✅ Array(LowCardinality(T)) - Array of low-cardinality elements
• ✅ Array(LowCardinality(Nullable(T))) - Array of nullable low-cardinality elements
• ✅ LowCardinality(Nullable(T)) - Low-cardinality column with nullable values

References:

• ClickHouse Issue #1062
  • Arrays cannot be nullable
• ClickHouse Issue #42456
  • LowCardinality cannot be inside Nullable

Re-exports

pub use array::ColumnArray;

pub use array::ColumnArrayT;

pub use date::ColumnDate;

pub use date::ColumnDate32;

pub use date::ColumnDateTime;

pub use date::ColumnDateTime64;

pub use decimal::ColumnDecimal;

pub use enum_column::ColumnEnum16;

pub use enum_column::ColumnEnum8;

pub use ipv4::ColumnIpv4;

pub use ipv6::ColumnIpv6;

pub use lowcardinality::ColumnLowCardinality;

pub use map::ColumnMap;

pub use nothing::ColumnNothing;

pub use nullable::ColumnNullable;

pub use string::ColumnFixedString;

pub use string::ColumnString;

pub use tuple::ColumnTuple;

pub use uuid::ColumnUuid;

pub use uuid::Uuid;

pub use numeric::*;

Modules

array

Array column type (Array(T)). Array column implementation

column_value

Column value extraction and insertion helpers. ColumnValue - A value extracted from or to be inserted into a column

date

Date and DateTime column types. Date and DateTime column implementations

decimal

Decimal column types (Decimal32, Decimal64, Decimal128).

enum_column

Enum8 and Enum16 column types. Enum8 and Enum16 column implementations.

geo

Geo type helpers (Point, Ring, Polygon, MultiPolygon). Geo type helpers for ClickHouse geo column types.

ipv4

IPv4 column type.

ipv6

IPv6 column type.

lowcardinality

LowCardinality column type (dictionary encoding). LowCardinality column implementation (dictionary encoding)

map

Map column type (Map(K, V)). Map column implementation.

nothing

Nothing/Void column type. Nothing/Void column implementation.

nullable

Nullable column type (Nullable(T)). Nullable column implementation

numeric

Numeric column types (integers, floats, bool). Numeric column implementations

string

String and FixedString column types. String column implementations

tuple

Tuple column type (Tuple(T1, T2, ...)). Tuple column implementation.

uuid

UUID column type. UUID column implementation.

Traits

Column

Base trait for all column types Note: We use byte buffers instead of generic readers/writers to make the trait dyn-compatible

ColumnIter

Trait for columns that support iteration over their values.

ColumnTyped

Helper trait for column types that can be downcasted

Type Aliases

ColumnRef

Reference to a column (using Arc for cheap cloning)