仅在先前记录具有特定值时显示记录

Question

I'm trouble shooting a certain business proces and i'm able to follow the flow in a database. I've found the error message I want to look into, but only in case of a certain flow.

My problem is how to achieve that in SQL.

For example

Source      Statement
--------    ------------
PORT        Cannot create
APP         No active visit
GIK         OIK
APP         No active visit

Now I only want to have the record with statement 'No active visit', if the previous record has a Source value "GIK".

How do I achieve that in SQL? I'm working in SSMS btw.

greets, Stoney

Answer 1

You can use lag() :

select t.*
from (select t.*,
             lag(Source) over (order by ?) as prev_source
      from table t
     ) t
where Statement = 'No active visit' and prev_source = 'GIK';

If lag() will not support then you can use apply :

select t.*
from table t cross apply
     (select top (1) t1.*
      from table t1 
      where t1.<identity_col> < t.<identity_col>
      order by t1.<identity_col> desc
     ) t1
where t.Statement = 'No active visit' and t1.source = 'GIK';

SQL tables represent unordered sets. If you want a specific ordering in the result set, you need one ordering column. So, use column name instead of ? that specify your column ordering.