Querying sequences of rows in SQL

Question

Suppose I am storing events associated with users in a table as follows (with dt standing in for the timestamp of the event):

Answer 1

For Oracle (version 11g R2):

By chance if you are using Oracle DB 11g R2, take look at listagg. The below code should work, but I haven't tested. The point is: you can use listagg.

SQL> select user,
  2         listagg( event, '' ) 
  3         within group (order by dt) events
  4     from users
  5    group by user
  6    order by dt
  7   /

     USER   EVENTS
---------  --------------------
1          ADBCB
2          BBAAC

In prior versions you can do with CONNECT BY clause. More details on listagg.