The UNCOMPRESS() function decompresses a "Binary string" and returns the result as a character string.
This function requires MySQL or MariaDB to be compiled with a compression library such as zlib, otherwise the return value is always NULL.
If the "Binary string" contains no characters, the function returns an empty string.
If the "Binary string" is invalid and cannot be decompressed, the function returns NULL.
If the value of the "Binary string" is NULL, the UNCOMPRESS() function returns NULL.
Strings can be compressed with the COMPRESS() function.