MariaDB UNCOMPRESS() Function

In MariaDB, UNCOMPRESS() is a built-in function that decompresses strings compressed by the COMPRESS() function.

MariaDB UNCOMPRESS() Syntax

Here is the syntax of the MariaDB UNCOMPRESS() function:

UNCOMPRESS(str_to_uncompress)

Parameters

str_to_uncompress

Required. A string to decompress.

If you provide the wrong number of parameters, MariaDB will report an error: ERROR 1582 (42000): Incorrect parameter count in the call to native function 'UNCOMPRESS'.

Return value

The MariaDB UNCOMPRESS() function decompresses the specified string str_to_uncompress and returns the result as a binary string.

If the argument is NULL, the MariaDB UNCOMPRESS() function returns NULL.

Check availability

The MariaDB UNCOMPRESS() function requires MariaDB to be compiled with a compression library such as zlib. If MariaDB has not been compiled with such a compression library, UNCOMPRESS() will not work, and it will return NULL.

To determine whether the UNCOMPRESS() function works correctly in the current MariaDB database server, use system variables have_compress.

This statement returns whether the current MariaDB database server supports compression:

SELECT @@have_compress;

Output:

+-----------------+
| @@have_compress |
+-----------------+
| YES             |
+-----------------+

If the server has access to the zlib compression library, the result is YES YES, otherwise the result will be NO.

MariaDB UNCOMPRESS() Examples

Basic usage

Here’s a basic example:

SELECT UNCOMPRESS(COMPRESS('Hello'));

Output:

+-------------------------------+
| UNCOMPRESS(COMPRESS('Hello')) |
+-------------------------------+
| Hello                         |
+-------------------------------+

NULL

If the argument is NULL, the MariaDB UNCOMPRESS() function returns NULL.

SELECT UNCOMPRESS(null);

Output:

+------------------+
| UNCOMPRESS(null) |
+------------------+
| NULL             |
+------------------+

Conclusion

In MariaDB, UNCOMPRESS() is a built-in function that decompresses strings compressed by the COMPRESS() function.