Hi,

Here is the sample code to create or generate a CSV file using apex code. The below code will query all SetupAuditTrail object records and stored the generated CSV file in document object folder. 

Usually Setup Audit Log in salesforce will provide only last six month of data. But when we need a specific range of logs, then we have to go for a custom logic. 

The below query will provide specific date range of Audit logs,

SELECT CreatedDate, CreatedBy.Username, Display, Section, Action, DelegateUser FROM SetupAuditTrail WHERE CreatedDate >= 2016-09-10T00:00:00Z AND CreatedDate <= 2016-10-01T00:00:00Z ORDER BY CreatedDate DESC

Sample Batch Code:

global class SetupAuditTrailBatch implements Database.Batchable<sObject>, Database.Stateful {
   
    global String csvColumnHeader;
    global List<String> csvRowValues = new List<String>();
   
    global Database.QueryLocator start(Database.BatchableContext BC){
        //Query all SetupAuditTrail records.
        String query = 'SELECT CreatedDate, CreatedBy.Username, Display, Section, Action, DelegateUser, CreatedById, CreatedBy.Name FROM SetupAuditTrail ORDER BY CreatedDate DESC';
        return Database.getQueryLocator(query);
    }
   
    global void execute(Database.BatchableContext BC, List<sObject> scope){
        //Process retrieved SetupAuditTrail records and format field values.
        for(SetupAuditTrail currSetupAudit : (List<SetupAuditTrail>) scope){
            String formattedDate = currSetupAudit.CreatedDate.format('M/d/yyyy h:mm:ss a z');
            String userName = currSetupAudit.CreatedBy.Username != null ? currSetupAudit.CreatedBy.Username : '';
            String displayVal = currSetupAudit.Display != null ? String.valueOf(currSetupAudit.Display).escapeCsv() : '';
            String sectionVal = currSetupAudit.Section != null ? currSetupAudit.Section : '';
            String delegateUser = currSetupAudit.DelegateUser != null ? currSetupAudit.DelegateUser : '';
           
            String rowStr = formattedDate + ',' + userName + ',' + displayVal + ',' + sectionVal + ','+ delegateUser;
            csvRowValues.add(rowStr);
        }
    }
   
    global void finish(Database.BatchableContext BC){
        List<Folder> folders = [SELECT Id, Name FROM Folder WHERE Name = 'Setup Audit Trail Logs'];
       
        if(!folders.isEmpty()){
            String documentName = 'SetupAuditTrailLog-'+ Datetime.now().format('MMM') + Datetime.now().year();
            csvColumnHeader = 'Date, User, Action, Section, Delegate User\n';
            String csvFile = csvColumnHeader + String.join(csvRowValues,'\n');
           
            // Insert the generated CSV file in Document object under "Setup Audit Trail Logs".
            Document doc = new Document(Name = documentName, Body = Blob.valueOf(csvFile), FolderId = folders[0].Id, Type = 'csv', ContentType='application/vnd.ms-excel');
            insert doc;
        }
    }
}

Hope this helps.

Kindly mark this as solved if the reply was helpful.

Thanks,
Nagendra