Encoding

Notice: Some of the examples below are referenced from ClickHouse Documentation but have been adapted and modified to work in ByConity.

UUIDNumToString

Accepts a FixedString(16) value, and returns a string containing 36 characters in text format.

Syntax

UUIDNumToString(FixedString(16))

Arguments

• a FixedString(16) value

Returned value

• String.

Example

SELECT
    'a/<@];!~p{jTj={)' AS bytes,
    UUIDNumToString(toFixedString(bytes, 16)) AS uuid

┌─bytes────────────┬─uuid─────────────────────────────────┐
│ a/<@];!~p{jTj={) │ 612f3c40-5d3b-217e-707b-6a546a3d7b29 │
└──────────────────┴──────────────────────────────────────┘

UUIDStringToNum

Accepts a string containing 36 characters in the format xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx , and returns it as a set of bytes in a FixedString(16).

Syntax

UUIDStringToNum(String)

Arguments

• a string in uuid format

Returned value

• FixedString(16)

Example

SELECT
    '612f3c40-5d3b-217e-707b-6a546a3d7b29' AS uuid,
    UUIDStringToNum(uuid) AS bytes

┌─uuid─────────────────────────────────┬─bytes────────────┐
│ 612f3c40-5d3b-217e-707b-6a546a3d7b29 │ a/<@];!~p{jTj={) │
└──────────────────────────────────────┴──────────────────┘

bitmaskToArray

Accepts an integer. Returns an array of UInt64 numbers containing the list of powers of two that total the source number when summed. Numbers in the array are in ascending order.

Syntax

bitmaskToArray(num)

Arguments

• num – an integer

Returned value

• an array of UInt64 numbers containing the list of powers of two that total the source number when summed.

Example

SELECT bitmaskToArray(1), bitmaskToArray(3), bitmaskToArray(4)

┌─bitmaskToArray(1)─┬─bitmaskToArray(3)─┬─bitmaskToArray(4)─┐
│ [1]               │ [1, 2]            │ [4]               │
└───────────────────┴───────────────────┴───────────────────┘

1 = power(2,0) 3 = power(2,0) + power(2,1) 4 = power(2,2)

bitmaskToList

Accepts an integer. Returns a string containing the list of powers of two that total the source number when summed. They are comma-separated without spaces in text format, in ascending order.

Syntax

bitmaskToList(num)

Arguments

• num – an integer

Returned value

• a string containing the list of powers of two that total the source number when summed

Example

SELECT bitmaskToList(1), bitmaskToList(3), bitmaskToList(4)

┌─bitmaskToList(1)─┬─bitmaskToList(3)─┬─bitmaskToList(4)─┐
│ 1                │ 1,2              │ 4                │
└──────────────────┴──────────────────┴──────────────────┘

1 = power(2,0) 3 = power(2,0) + power(2,1) 4 = power(2,2)

hex

Returns a string containing the argument’s hexadecimal representation.

Syntax

hex(arg)

The function is using uppercase letters A-F and not using any prefixes (like 0x ) or suffixes (like h ).

For integer arguments, it prints hex digits (“nibbles”) from the most significant to least significant (big endian or “human readable” order). It starts with the most significant non-zero byte (leading zero bytes are omitted) but always prints both digits of every byte even if leading digit is zero.

Values of type Date and DateTime are formatted as corresponding integers (the number of days since Epoch for Date and the value of Unix Timestamp for DateTime).

For String and FixedString , all bytes are simply encoded as two hexadecimal numbers. Zero bytes are not omitted.

危险

Values of floating point and Decimal types are encoded as their representation in memory. As we support little endian architecture, they are encoded in little endian. Zero leading/trailing bytes are not omitted.

Arguments

• arg — A value to convert to hexadecimal. Types: String, UInts, Date or DateTime. TODO: FLOAT & Decimal is not support by cnch

Returned value

• A string with the hexadecimal representation of the argument. Type: String .

Example

SELECT hex('a'), hex(1), hex(toDate('2019-01-01')), hex(toDateTime('2019-01-01 00:00:00'))

┌─hex('a')─┬─hex(1)─┬─hex(toDate('2019-01-01'))─┬─hex(toDateTime('2019-01-01 00:00:00'))─┐
│ 61       │ 01     │ 45E9                      │ 5C2A3D00                               │
└──────────┴────────┴───────────────────────────┴────────────────────────────────────────┘

TODO: NOT SUPPORT BY CNCH

SELECT hex(toFloat32(number)) as hex_presentation FROM numbers(15, 2);

┌─hex_presentation─┐
│ 00007041         │
│ 00008041         │
└──────────────────┘

SELECT hex(toFloat64(number)) as hex_presentation FROM numbers(15, 2);

┌─hex_presentation─┐
│ 0000000000002E40 │
│ 0000000000003040 │
└──────────────────┘

unhex

Performs the opposite operation of hex. It interprets each pair of hexadecimal digits (in the argument) as a number and converts it to the byte represented by the number. The return value is a binary string (BLOB).

If you want to convert the result to a number, you can use the reverse and reinterpretAs<Type> functions.

!!! note "Note"

If unhex is invoked from within the gateway-client , binary strings display using UTF-8.

Syntax

unhex(arg)

Arguments

• arg — A string containing any number of hexadecimal digits. Type: String. Supports both uppercase and lowercase letters A-F . The number of hexadecimal digits does not have to be even. If it is odd, the last digit is interpreted as the least significant half of the 00-0F byte. If the argument string contains anything other than hexadecimal digits, some implementation-defined result is returned (an exception isn’t thrown). For a numeric argument the inverse of hex(N) is not performed by unhex().

Returned value

• A binary string (BLOB). Type: String.

Example

SELECT unhex('303132'), unhex('4D7953514C');

┌─unhex('303132')─┬─unhex('4D7953514C')─┐
│ 012             │ MySQL               │
└─────────────────┴─────────────────────┘

SELECT reinterpretAsUInt64(reverse(unhex('FFF'))) AS num;

┌─num──┐
│ 4095 │
└──────┘