Question

I have table (already sorted) in SQL server with the following:

stringname
==========
stringA
stringA
stringB
stringB
stringA
stringC
stringC
stringC
stringA

I would like to output the following:

stringname previous_stringname count
========== =================== =====
stringA    NULL                1
stringA    stringA             1
stringA    stringB             1
stringA    stringC             1
stringB    stringA             1
stringB    stringB             1
stringC    stringA             1
stringC    stringC             2

That is, for each stringname in the original table and for each of that stringname’s previous entry, I would like to output it with the number of times it had each previous string (with NULL for the first entry).

How would I write an SQL query for this?

I am using SQL Server 2008.

Answer 1

Recursion is not necessary; just use:

select b.stringname as stringname, a.stringname as previous_stringname
    into #tmp
    from (select stringname, row_number() over (order by id /* $/0 */) as row from testing) a
    right outer join (select stringname, row_number() over (order by id /* $/0 */) as row from testing) b
    on a.row = b.row - 1;
select *, count(*) as [count] from #tmp group by stringname, previous_stringname;