Column Types
See Data Types for general reference.
Numeric types
Numeric types encoding matches memory layout of little endian CPUs like AMD64 or ARM64.
This allows to implement very efficient encoding and decoding.
Integers
String of Int and UInt of 8, 16, 32, 64, 128 or 256 bits, in little endian.
Floats
Float32 and Float64 in IEEE 754 binary representation.
String
Just an array of String, i.e. (len, value).
FixedString(N)
An array of N-byte sequences.
IP
IPv4 is alias of UInt32 numeric type and represented as UInt32.
IPv6 is alias of FixedString(16) and represented as binary directly.
Tuple
Tuple is just an array of columns. For example, Tuple(String, UInt8) is just two columns encoded continuously.
Map
Map(K, V) consists of three columns: Offsets ColUInt64, Keys K, Values V.
Rows count in Keys and Values column is last value from Offsets.
Array
Array(T) consists of two columns: Offsets ColUInt64, Data T.
Rows count in Data is last value from Offsets.
Nullable
Nullable(T) consists of Nulls ColUInt8, Values T with same rows count.
UUID
Alias of FixedString(16), UUID value represented as binary.
Enum
Alias of Int8 or Int16, but each integer is mapped to some String value.
Low Cardinality
LowCardinality(T) consists of Index T, Keys K,
where K is one of (UInt8, UInt16, UInt32, UInt64) depending on size of Index.
Bool
Alias of UInt8, where 0 is false and 1 is true.