GoogleSQL for Spanner supports compression functions.

Compression functions compress or decompress bytes or string values using theZstandard (Zstd) lossless data compression algorithm.

Function list

ZSTD_COMPRESS

ZSTD_COMPRESS(string_or_bytes_value,level=>3)

Description

CompressesSTRING orBYTES input intoBYTES output using the Zstandard (Zstd) losslessdata compression algorithm.

Arguments:

• string_or_bytes_value: The SQL value to compress.
• level: Optional. The Zstd compression level. The default is 3. You can setlevel to an integer value between -5 and 22. A higher value results in a better compression ratio at the cost of slower performance.

Return type

BYTES: Base64-encoded bytes.

Example

SELECTZSTD_COMPRESS('string_value')ASresult;/*------------------------------+ | result                       | +------------------------------+ | KLUv/SAMYQAAc3RyaW5nX3ZhbHVl | +------------------------------*/

SELECTZSTD_COMPRESS(b'bytes_value',level=>1);/*------------------------------+ | result                       | +------------------------------+ | KLUv/SALWQAAYnl0ZXNfdmFsdWU= | +------------------------------*/

This function returnsNULL if the input isNULL:

SELECTZSTD_COMPRESS(NULL)ASresult;/*------------+ | result     | +------------+ | NULL       | +------------*/

ZSTD_DECOMPRESS_TO_BYTES

ZSTD_DECOMPRESS_TO_BYTES(bytes_value,size_limit=>1024*1024*1024)

Description

DecompressesBYTES input intoBYTES using theZstandard (Zstd) lossless data compression algorithm.

Arguments:

• bytes_value: The bytes to decompress.
• size_limit: Optional. The size limit of returned decompressed bytes. The default value is one GiB. You can set this limit to a lower value to minimize the risk ofZSTD_DECOMPRESS_TO_BYTES causing server memory issues.

Return type

BYTES: Base64-encoded bytes.

Example

SELECTZSTD_DECOMPRESS_TO_BYTES(ZSTD_COMPRESS(b'bytes'))ASresult;/*------------+ | result     | +------------+ | Ynl0ZXM=   | +------------*/

If compressed bytes exceed thesize_limit value,ZSTD_DECOMPRESS_TO_BYTESreturns an error:

SELECTZSTD_DECOMPRESS_TO_BYTES(ZSTD_COMPRESS(b'bytes'),size_limit=>1)ASresult;Statementfailed:ZSTDoutputistoolarge:(5bytes) >limit(1bytes)

This function returnsNULL if the input isNULL:

SELECTZSTD_DECOMPRESS_TO_BYTES(NULL)ASresult;/*------------+ | result     | +------------+ | NULL       | +------------*/

ZSTD_DECOMPRESS_TO_STRING

ZSTD_DECOMPRESS_TO_STRING(bytes_value,size_limit=>1024*1024*1024)

Description

DecompressBYTES input intoSTRING output using theZstandard (Zstd) lossless data compression algorithm.

Arguments:

• bytes_value: The bytes to decompress.
• size_limit: Optional. The size limit of returned decompressed string. The default value is one GiB. You can set this limit to a lower value to minimize the risk ofZSTD_DECOMPRESS_TO_STRING causing server memory issues.

Return type

STRING

Example

SELECTZSTD_DECOMPRESS_TO_STRING(ZSTD_COMPRESS('zstd'))ASresult;/*----------+ | result   | +----------+ | "zstd"   | +----------*/

If compressed bytes exceed thesize_limit value,ZSTD_DECOMPRESS_TO_STRINGreturns an error:

SELECTZSTD_DECOMPRESS_TO_STRING(ZSTD_COMPRESS('zstd'),size_limit=>1)ASresult;Statementfailed:ZSTDoutputistoolarge:(4bytes) >limit(1bytes)

This function returnsNULL if the input isNULL:

SELECTZSTD_DECOMPRESS_TO_STRING(NULL)ASresult;/*------------+ | result     | +------------+ | NULL       | +------------*/