Transform Functions

NOTE

Verification Status: Tested and Verified against rekuiper engine with live telemetry stream load on 2026-10-14 20:50:00 UTC.
Scorecard: 13 Verified, 0 Unsupported, 0 Broken:

• Verified (13): cast, convert_tz, to_seconds, encode (base64), base64_encode, decode (base64), base64_decode, compress (zlib/gzip/flate/zstd), decompress (zlib/gzip/flate/zstd), trunc, chr, hex2dec, dec2hex.

Transform functions convert data types, encode payloads, and apply compression algorithms.

CAST

cast(col, dataType)

Converts a value to the specified target data type. Supported target types include: bigint, float, string, boolean, bytea, and datetime.

Cast to datetime

When casting a value to datetime, the engine applies the following conversion rules:

1. If the input is already a datetime value, the function returns the value directly.
2. If the input is bigint or float, the function interprets the number as milliseconds since January 1, 1970 00:00:00 UTC.
3. If the input is string, the function parses the format into a datetime value. For supported time formats, refer to TimeFormats.
4. Conversions from other types are not supported.

CONVERT_TZ

convert_tz(col, "Asia/Shanghai")

Converts a timestamp to the specified target time zone. Specify time zones using the IANA Time Zone Database format. The default time zone is UTC. Specify Local to apply the host system time zone.

NOTE

In Alpine Linux containers, you must install the tzdata package (for example, apk add tzdata) to provide time zone database files.

TO_SECONDS

to_seconds(col)

Converts col to a datetime value and returns Unix epoch time as the number of elapsed seconds since January 1, 1970 00:00:00 UTC.

ENCODE

encode(col, encodeType)
base64_encode(col)

Encodes binary or string payload data into a string representation using the specified encoding scheme. Currently, the engine supports "base64".

base64_encode(col) is a convenient single-argument function equivalent to encode(col, "base64").

Example

SELECT base64_encode(payload) AS b64, encode(payload, "base64") AS b64_alt FROM demo;

Given input {"payload": "Hello, Rekuiper!"}:

{
  "b64": "SGVsbG8sIFJla3VpcGVyIQ==",
  "b64_alt": "SGVsbG8sIFJla3VpcGVyIQ=="
}

DECODE

decode(col, encodeType)
base64_decode(col)

Decodes an encoded string into its original representation using the specified decoding scheme. Currently, the engine supports "base64".

base64_decode(col) is a convenient single-argument function equivalent to decode(col, "base64").

Example

SELECT base64_decode(b64) AS original_text FROM demo;

Given input {"b64": "SGVsbG8sIFJla3VpcGVyIQ=="}:

{
  "original_text": "Hello, Rekuiper!"
}

NOTE

Compatibility & Safety Note: Non-Crashing Null Safety in DECODE In legacy eKuiper, unhandled decoding errors or unmapped targets in value decoders could panic at runtime when no default fallback was provided. rekuiper safely returns null on decode failures without panicking.

Why we chose this difference: Returning null follows SQL standards for conversion errors and prevents corrupt or malformed incoming sensor records from aborting active stream processing.

COMPRESS

compress(input, method)

Compresses an input string or binary payload using the specified algorithm. Supported methods include 'zlib', 'gzip', 'flate', and 'zstd'.

DECOMPRESS

decompress(input, method)

Decompresses compressed payload data using the specified algorithm. Supported methods include 'zlib', 'gzip', 'flate', and 'zstd'.

TRUNC

trunc(dec, int)

Truncates the decimal number dec to the number of decimal places specified by int. If the second argument is less than 0, the function uses 0. If greater than 34, the function uses 34. The function removes trailing zeros from the result.

CHR

chr(col)

Returns the ASCII character corresponding to the specified integer code.

NOTE

Compatibility & Safety Note: Panic-Free Codepoint Validation in CHR Legacy eKuiper crashes on negative or out-of-range integer values passed to chr(). rekuiper validates codepoint bounds (0 to 127 for ASCII, valid Unicode scalar values) and safely returns null for invalid or negative inputs without crashing.

Why we chose this difference: Preventing server process crashes on abnormal sensor numbers is essential for edge gateways operating autonomously in unattended environments.

HEX2DEC

hex2dec(col)

Converts a hexadecimal string into its decimal integer value. The argument must be a string. Values such as "0x10" or "10" convert to integer 16.

DEC2HEX

dec2hex(col)

Converts a decimal integer into a hexadecimal string with a "0x" prefix. For example, integer 16 converts to "0x10".