Native protocol column types

See Data Types for general reference.

Tip

Numeric types encoding matches memory layout of little endian CPUs like AMD64 or ARM64, allowing very efficient encoding and decoding.

Type	Encoding
Integers (Int/UInt)	8, 16, 32, 64, 128 or 256 bits in little endian
Floats (Float32/Float64)	IEEE 754 binary representation
String	Array of strings as (len, value)
FixedString(N)	Array of N-byte sequences
IPv4	Alias of UInt32, represented as UInt32
IPv6	Alias of FixedString(16), represented as binary
Tuple	Array of columns encoded continuously. Example: Tuple(String, UInt8) = two continuous columns
Map	Map(K, V) = three columns: Offsets ColUInt64, Keys K, Values V. Row count in Keys/Values = last Offsets value
Array	Array(T) = two columns: Offsets ColUInt64, Data T. Row count in Data = last Offsets value
Nullable	Nullable(T) = two columns: Nulls ColUInt8, Values T with same row count. Nulls is mask: 1=null, 0=value
UUID	Alias of FixedString(16), represented as binary
Enum	Alias of Int8 or Int16, each integer mapped to a String value
LowCardinality	LowCardinality(T) = two columns: Index T, Keys K where K is UInt8/16/32/64. Index contains unique values, Keys contains indexes into Index
Bool	Alias of UInt8: 0=false, 1=true

Example: Nullable encoding

To encode [null, "", "hello", null, "world"]:
  Values: ["", "", "hello", "", "world"] (len: 5)
  Nulls:  [ 1,  0,       0,  1,       0] (len: 5)

Example: LowCardinality encoding

To encode ["Eko", "Eko", "Amadela", "Amadela", "Amadela", "Amadela"]:
  Index: ["Eko", "Amadela"] (String)
  Keys:  [0, 0, 1, 1, 1, 1] (UInt8)