A developer would use the LookupRows function instead of the Lookup AMPscript function to return a complete rowset from the data extension (A). The LookupRows function retrieves all rows that match a specified criterion, returning a rowset that can be further processed or iterated over in AMPscript. In contrast, the Lookup function retrieves only a single field value from the first row that matches the specified criteria.
References:
Salesforce Marketing Cloud AMPscript Guide
Salesforce Marketing Cloud AMPscript Functions

Before importing zipped files into a Data Extension, a File Transfer activity is needed to unzip the files on the Marketing Cloud Enhanced FTP server. This activity moves and decompresses the files to make them available for import.
* File Transfer Activity: This activity is used to move files from one location to another and to unzip compressed files.
Salesforce File Transfer Activity

Content Builder uses the REST API to manage content within Salesforce Marketing Cloud. The REST API allows developers to create, update, retrieve, and delete content assets, making it suitable for cross-channel campaign functions.
Salesforce Content Builder API

To trigger an email send in Marketing Cloud when a purchase is made on a website, you can use either the REST API or the SOAP API. Both APIs provide methods to send triggered emails.
* REST API: The REST API can be used to trigger emails by making a call to the /messaging/v1
/messageDefinitionSends/{key}/send endpoint.
* SOAP API: The SOAP API can also be used to trigger sends by utilizing the TriggeredSend object.
Salesforce Marketing Cloud REST API
Salesforce Marketing Cloud SOAP API

The SQL statement in question does not return any records because it is joining on the EmailAddress field, which is not present in the _Bounce Data View. The correct approach is to join using the SubscriberKey (or SubscriberID). Here is the corrected SQL statement:
SELECT s.EmailAddress, s.SubscriberKey, b.JobID, b.EventDate, b.SMTPBounceReason FROM
_Subscribers s JOIN _Bounce b ON s.SubscriberKey = b.SubscriberKey WHERE b.EventDate > DateAdd (DAY, -30, GETDATE()) This ensures that the join is based on the SubscriberKey, which is a common field in both data views.
References:
Salesforce Marketing Cloud Data Views
Query Activity Best Practices