Decode the Message

You're provided with two strings: key and message. Key represents a cipher key, and message is the secret message you need to decode. The decoding process involves the following steps:

1. Utilize the first occurrence of all 26 lowercase English letters in key to establish the order of the substitution table.
2. Align the substitution table with the regular English alphabet.
3. Substitute each letter in the message using the established table.
4. Spaces (' ') remain unchanged.

For instance, given key = "happy boy" (the actual key should contain at least one instance of each letter in the alphabet), we derive a partial substitution table as follows: ('h' -> 'a', 'a' -> 'b', 'p' -> 'c', 'y' -> 'd', 'b' -> 'e', 'o' -> 'f').

Your task is to print the decoded message.