Module types 

ClickHouse type system and type string parser.

ClickHouse Type System

This module implements the ClickHouse type system for the native TCP protocol.

ClickHouse Documentation References

Numeric Types

• Integer Types
  • Int8/16/32/64/128, UInt8/16/32/64/128
• Floating-Point Types
  • Float32, Float64
• Decimal Types
  • Decimal, Decimal32/64/128

String Types

• String
  • Variable-length strings
• FixedString
  • Fixed-length binary strings

Date and Time Types

• Date - Days since 1970-01-01
• Date32
  • Extended date range
• DateTime
  • Unix timestamp (UInt32)
• DateTime64
  • High precision timestamp (Int64)

Compound Types

• Array - Arrays of elements
• Tuple - Fixed-size collections
• Map - Key-value pairs

Special Types

• Nullable
  • Adds NULL support to any type
• LowCardinality
  • Dictionary encoding for compression
• Enum8/Enum16
  • Enumerated values
• UUID - Universally unique identifiers
• IPv4/IPv6
  • IP addresses

Geo Types

• Point - 2D point (Tuple(Float64, Float64))
• Ring - Array of Points
• Polygon - Array of Rings
• MultiPolygon
  • Array of Polygons

Type Nesting Rules

ClickHouse enforces strict type nesting rules (Error code 43: ILLEGAL_TYPE_OF_ARGUMENT):

✅ Allowed:

• Array(Nullable(T)) - Array where each element can be NULL
• LowCardinality(Nullable(T)) - Dictionary-encoded nullable values
• Array(LowCardinality(T)) - Array of dictionary-encoded values
• Array(LowCardinality(Nullable(T))) - Combination of all three

❌ NOT Allowed:

• Nullable(Array(T)) - Arrays themselves cannot be NULL (use empty array instead)
• Nullable(LowCardinality(T)) - Wrong nesting order
• Nullable(Nullable(T)) - Double-nullable is invalid

For more details, see the column module documentation.

Structs

EnumItem

Enum item for Enum8/Enum16 types, mapping a name to its integer value.

TypeAst

Abstract Syntax Tree for a type definition Mirrors C++ struct TypeAst

Enums

Type

ClickHouse type definition, representing both simple and parametric types.

TypeCode

Type code enumeration matching ClickHouse types

TypeMeta

TypeAst meta-type classification Mirrors C++ TypeAst::Meta

Traits

ToType

Trait for mapping Rust primitive types to ClickHouse types Equivalent to C++ Type::CreateSimple<T>() template specializations

Functions

parse_type_name

Parse a type name and return cached AST Mirrors C++ const TypeAst* ParseTypeName(const std::string& type_name)

Type Aliases

TypeRef

Reference-counted shared pointer to a Type.