Here is what is on my old server done by another guru on postfix many years ago.
---------------------
I have a table "users" with a destination field for the mailbox called
"to_ext"
I created 2 files to be able to forward email to external addresses
using wildcard.
Let me know if you implement this so I can have you update my server.
I really would like to rite that old server but I have several forwarded
domains I can not do on my ired pro.

Here are some of the records:
many to many with wildcard

email              to_ext                    status      domain_id.....
%@domain1.tld      @domain.elsewhere.tld     Forward     1

result
user1@domain1.tld  is forwarded to    user1@domain.elsewhere.tld
user2@domain1.tld  is forwarded to    user2@domain.elsewhere.tld

email              to_ext                    status      domain_id.....
%@domain1.tld      user1@domain.elsewhere.tld     Forward     1

Any user in domain1.tld is forwarded to user1@domain.elsewhere.tld

domain.elsewhere.tld can be local or any domain on the internet

Status:    The status this user will have,

Normal = delivery locally to the mailbox set in To_External field,
Forward = (to forward this email to somewhere else) MUST enter data into
To External field, ie: email address to forward the email to. Moved (to
alert the sender this email has moved to somewhere else) MUST enter data
into To External field, ie:new_email@address.com or unknown
(* Mail Box)

To External:    This field should have the the Mail Box directory name the
mail should be delivered to.
* If left blank the system will automatically use the Username. It also
should contain data if the status field is either Forward
(Email@address.to.forward) or Moved to (tipically UNKNOWN) Email will
bounce back to sender with this notation.
Use this field to alias the user to some other local mailbox, ie:
postmaster@domain.tld to user "jdoe" or abuse@domain.tld to user mailbox
"lsmith".(The local mailbox MUST exist)

here is my mysql query files.

virtual_forwards.cf
# Database lookup for "Forwarded Virtual Aliases", eg. email destinations
# in virtual domains that we host, but which are to be forwarded
someplace else
# Key is Recipient Address
# Result is remote email address
# Using the LIKE statement reversed allows us to put SQL wildcards (%,_)
# into the database...
user         = postfix
password     = xxxxxxxxx
dbname       = postfix2
hosts        = 127.0.0.1
query        = SELECT users.to_ext FROM domains,users WHERE
users.status='forward' AND domains.type='virtual' AND domains.id =
users.domain_id AND '%s' LIKE users.email
----------------------------------
relocated.cf
# Database lookup "Relocated" adresses.
# Key is Recipient Address
#
# Using the LIKE statement reversed allows us to put SQL wildcards (%,_)
# into the database...
# the to_ext column contains the new email address or any message like the word "UNKNOWN"
#The email will bounce with a message:
#Recipient address rejected: User has moved to "UNKNOWN"

user         = postfix
password     = xxxxxxxxxxxx
dbname       = postfix2
hosts        = 127.0.0.1
query        = SELECT users.to_ext FROM users WHERE users.status='moved'
AND '%s' LIKE users.email

Here is the portion of the main.cf file
# ADDRESS REDIRECTION (VIRTUAL DOMAIN)
#
# The VIRTUAL_README document gives information about the many forms
# of domain hosting that Postfix supports.
virtual_alias_maps =
proxy:mysql:$config_directory/mysql/virtual_aliases.cf,
proxy:mysql:$config_directory/mysql/virtual_forwards.cf
virtual_alias_domains =
proxy:mysql:$config_directory/mysql/virtual_domains.cf

# "USER HAS MOVED" BOUNCE MESSAGES
# See the discussion in the ADDRESS_REWRITING_README document.
relocated_maps = proxy:mysql:$config_directory/mysql/relocated.cf