SFMC Use AMPScript to see if user is in data extension

Question

I'm sending to a big list and it has groups of users set up as Data Extensions. I want to do some dynamic content at time of send based on if the user is in a particular Data Extension. There is some overlap but I can deal with that with if/else. I was thinking of doing something like this:

%%[ IF UserIsInDataExtension("London_users") THEN ]%%
(Content for London segment)
%%[ ELSEIF UserIsInDataExtension("Birmingham_users")]%$
(Content for Birmingham segment)
%%[ ELSEIF UserIsInDataExtension("Never_purchased")]%%
(Content for Never purchased segment)
%%[ELSE]%%
(default content)
%%[ END ]%%

Is there something like this in AMPScript , and if there's nothing exactly like this then can I do something which attempts a lookup from the Data Extension as a way of seeing if the user is in it?

Answer 1

Sounds like your best bet might be to use the Lookup() AMPScript function. For example:

%%[

var @lookupEmailAddress 
set @lookupEmailAddress = AttributeValue("emailaddr")
set @InLondonUsers = Lookup("London_users", "emailAddress", "emailAddress", @lookupEmailAddress)

]%%

%%[ if not empty(@InLondonUsers) then ]%%
(Content for London segment)
%%[ endif ]%%

Reference: AMPScript Lookup() Function

Lookup(S1, S2, S3, S4)

Returns specified value from a data extension.

Arguments

S1 - The name of the data extension from which to return the specified value

S2 - Name of column from which to return a value

S3 - Name of column to match on to identify the row that contains the lookup value

S4 - Value to match S3 against

There are other ways to retrieve data from Data Extensions. You can find more code samples here on my blog.