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

I'm not at a computer to write code for this answer, but here's how I would go about a RegEx-based solution in SQL Server:

1. Build a string from the resultset. Something like http://blog.sqlauthority.com/2009/11/25/sql-server-comma-separated-values-csv-from-table-column/ should work if you omit the comma
2. Run your RegEx match against the resulting string. Unfortunately, SQL Server does not provide this functionality natively, however, you can use a CLR function for this purpose as described at http://www.ideaexcursion.com/2009/08/18/sql-server-regular-expression-clr-udf/

This should ultimately provide you with the functionality in SQL Server that your original question requests, however, if you're analyzing a very large dataset, this could be quite slow and there may be better ways to accomplish what you're looking for.