string-expression
The string to decompress. Binary values can also be passed to this function. This parameter is case sensitive, even in
case-insensitive databases.
compression-algorithm-alias
Alias (string) for the algorithm to use for decompression. The supported values are zip and gzip (both are based on the
same algorithm, but use different headers and trailers).
Zip is a widely supported compression algorithm. Gzip is compatible with the gzip utility on Unix, whereas the zip algorithm
is not.
If no algorithm is specified, the function attempts to detect which algorithm was used to compress the string. If the incorrect
algorithm is specified, or the correct algorithm cannot be detected, the string is not decompressed.
This function can be used to decompress a value that was compressed using the COMPRESS function.
You do not need to use the DECOMPRESS function on values that are stored in a compressed column. Compression and decompression
of values in a compressed column are handled automatically by the database server.
The following example uses the DECOMPRESS function to decompress values from the Attachment column of a fictitious table,
TableA:
SELECT DECOMPRESS ( Attachment, 'gzip' )
FROM TableA;
Since DECOMPRESS returns binary values, if the original values were of a character type, such as LONG VARCHAR, a CAST can
be applied to return human-readable values:
SELECT CAST ( DECOMPRESS ( Attachment, 'gzip' )
AS LONG VARCHAR ) FROM TableA;