Data types binary encoding specification

This specification describes the binary format that can be used for binary encoding and decoding of ClickHouse data types. This format is used in Dynamic column binary serialization and can be used in input/output formats RowBinaryWithNamesAndTypes and Native under corresponding settings.

The table below describes how each data type is represented in binary format. Each data type encoding consist of 1 byte that indicates the type and some optional additional information. var_uint in the binary encoding means that the size is encoded using Variable-Length Quantity compression.

ClickHouse data type	Binary encoding
`Nothing`	`0x00`
`UInt8`	`0x01`
`UInt16`	`0x02`
`UInt32`	`0x03`
`UInt64`	`0x04`
`UInt128`	`0x05`
`UInt256`	`0x06`
`Int8`	`0x07`
`Int16`	`0x08`
`Int32`	`0x09`
`Int64`	`0x0A`
`Int128`	`0x0B`
`Int256`	`0x0C`
`Float32`	`0x0D`
`Float64`	`0x0E`
`Date`	`0x0F`
`Date32`	`0x10`
`DateTime`	`0x11`
`DateTime(time_zone)`	`0x12<var_uint_time_zone_name_size><time_zone_name_data>`
`DateTime64(P)`	`0x13<uint8_precision>`
`DateTime64(P, time_zone)`	`0x14<uint8_precision><var_uint_time_zone_name_size><time_zone_name_data>`
`String`	`0x15`
`FixedString(N)`	`0x16<var_uint_size>`
`Enum8`	`0x17<var_uint_number_of_elements><var_uint_name_size_1><name_data_1><int8_value_1>...<var_uint_name_size_N><name_data_N><int8_value_N>`
`Enum16`	`0x18<var_uint_number_of_elements><var_uint_name_size_1><name_data_1><int16_little_endian_value_1>...><var_uint_name_size_N><name_data_N><int16_little_endian_value_N>`
`Decimal32(P, S)`	`0x19<uint8_precision><uint8_scale>`
`Decimal64(P, S)`	`0x1A<uint8_precision><uint8_scale>`
`Decimal128(P, S)`	`0x1B<uint8_precision><uint8_scale>`
`Decimal256(P, S)`	`0x1C<uint8_precision><uint8_scale>`
`UUID`	`0x1D`
`Array(T)`	`0x1E<nested_type_encoding>`
`Tuple(T1, ..., TN)`	`0x1F<var_uint_number_of_elements><nested_type_encoding_1>...<nested_type_encoding_N>`
`Tuple(name1 T1, ..., nameN TN)`	`0x20<var_uint_number_of_elements><var_uint_name_size_1><name_data_1><nested_type_encoding_1>...<var_uint_name_size_N><name_data_N><nested_type_encoding_N>`
`Set`	`0x21`
`Interval`	`0x22<interval_kind>` (see interval kind binary encoding)
`Nullable(T)`	`0x23<nested_type_encoding>`
`Function`	`0x24<var_uint_number_of_arguments><argument_type_encoding_1>...<argument_type_encoding_N><return_type_encoding>`
`AggregateFunction(function_name(param_1, ..., param_N), arg_T1, ..., arg_TN)`	`0x25<var_uint_version><var_uint_function_name_size><function_name_data><var_uint_number_of_parameters><param_1>...<param_N><var_uint_number_of_arguments><argument_type_encoding_1>...<argument_type_encoding_N>` (see aggregate function parameter binary encoding)
`LowCardinality(T)`	`0x26<nested_type_encoding>`
`Map(K, V)`	`0x27<key_type_encoding><value_type_encoding>`
`IPv4`	`0x28`
`IPv6`	`0x29`
`Variant(T1, ..., TN)`	`0x2A<var_uint_number_of_variants><variant_type_encoding_1>...<variant_type_encoding_N>`
`Dynamic(max_types=N)`	`0x2B<uint8_max_types>`
`Custom type` (`Ring`, `Polygon`, etc)	`0x2C<var_uint_type_name_size><type_name_data>`
`Bool`	`0x2D`
`SimpleAggregateFunction(function_name(param_1, ..., param_N), arg_T1, ..., arg_TN)`	`0x2E<var_uint_function_name_size><function_name_data><var_uint_number_of_parameters><param_1>...<param_N><var_uint_number_of_arguments><argument_type_encoding_1>...<argument_type_encoding_N>` (see aggregate function parameter binary encoding)
`Nested(name1 T1, ..., nameN TN)`	`0x2F<var_uint_number_of_elements><var_uint_name_size_1><name_data_1><nested_type_encoding_1>...<var_uint_name_size_N><name_data_N><nested_type_encoding_N>`
`JSON(max_dynamic_paths=N, max_dynamic_types=M, path Type, SKIP skip_path, SKIP REGEXP skip_path_regexp)`	`0x30<uint8_serialization_version><var_int_max_dynamic_paths><uint8_max_dynamic_types><var_uint_number_of_typed_paths><var_uint_path_name_size_1><path_name_data_1><encoded_type_1>...<var_uint_number_of_skip_paths><var_uint_skip_path_size_1><skip_path_data_1>...<var_uint_number_of_skip_path_regexps><var_uint_skip_path_regexp_size_1><skip_path_data_regexp_1>...`
`BFloat16`	`0x31`
`Time`	`0x32`
`Time64(P)`	`0x34<uint8_precision>`
`QBit(T, N)`	`0x36<element_type_encoding><var_uint_dimension>`
`QBit(T, N, stride)`	`0x37<element_type_encoding><var_uint_dimension><var_uint_stride>`

For type JSON byte uint8_serialization_version indicates the version of the serialization. Right now the version is always 0 but can change in future if new arguments will be introduced for JSON type.

For type QBit the 0x37 encoding is used only when stride differs from the dimension N. When stride == N (including when the third argument is written explicitly, as in QBit(Float32, 4, 4)) the type is canonicalized to the two-argument QBit(T, N) form and encoded as 0x36 above, so its binary encoding stays byte-identical to a non-strided QBit.

Interval kind binary encoding

The table below describes how different interval kinds of Interval data type are encoded.

Interval kind	Binary encoding
`Nanosecond`	`0x00`
`Microsecond`	`0x01`
`Millisecond`	`0x02`
`Second`	`0x03`
`Minute`	`0x04`
`Hour`	`0x05`
`Day`	`0x06`
`Week`	`0x07`
`Month`	`0x08`
`Quarter`	`0x09`
`Year`	`0x1A`

Aggregate function parameter binary encoding

The table below describes how parameters of AggregateFunction and SimpleAggregateFunction are encoded. The encoding of a parameter consists of 1 byte indicating the type of the parameter and the value itself.

Parameter type	Binary encoding
`Null`	`0x00`
`UInt64`	`0x01<var_uint_value>`
`Int64`	`0x02<var_int_value>`
`UInt128`	`0x03<uint128_little_endian_value>`
`Int128`	`0x04<int128_little_endian_value>`
`UInt256`	`0x05<uint256_little_endian_value>`
`Int256`	`0x06<int256_little_endian_value>`
`Float64`	`0x07<float64_little_endian_value>`
`Decimal32`	`0x08<var_uint_scale><int32_little_endian_value>`
`Decimal64`	`0x09<var_uint_scale><int64_little_endian_value>`
`Decimal128`	`0x0A<var_uint_scale><int128_little_endian_value>`
`Decimal256`	`0x0B<var_uint_scale><int256_little_endian_value>`
`String`	`0x0C<var_uint_size><data>`
`Array`	`0x0D<var_uint_size><value_encoding_1>...<value_encoding_N>`
`Tuple`	`0x0E<var_uint_size><value_encoding_1>...<value_encoding_N>`
`Map`	`0x0F<var_uint_size><key_encoding_1><value_encoding_1>...<key_encoding_N><value_encoding_N>`
`IPv4`	`0x10<uint32_little_endian_value>`
`IPv6`	`0x11<uint128_little_endian_value>`
`UUID`	`0x12<uuid_value>`
`Bool`	`0x13<bool_value>`
`Object`	`0x14<var_uint_size><var_uint_key_size_1><key_data_1><value_encoding_1>...<var_uint_key_size_N><key_data_N><value_encoding_N>`
`AggregateFunctionState`	`0x15<var_uint_name_size><name_data><var_uint_data_size><data>`
`Negative infinity`	`0xFE`
`Positive infinity`	`0xFF`

Interval kind binary encoding​

Aggregate function parameter binary encoding​

Interval kind binary encoding

Aggregate function parameter binary encoding