SQL - Combining 3 rows per group in a logging scenario - sql

Question

I have reworked our API's logging system to use Azure Table Storage from using SQL storage for cost and performance reasons. I am now migrating our legacy logs to the new system. I am building a SQL query per table that will map the old fields to the new ones, with the intention of exporting to CSV then importing into Azure.
So far, so good. However, one artifact of the previous system is that it logged 3 times per request - call begin, call response and call end - and the new one logs the call as just one log (again, for cost and performance reasons).
Some fields common are common to all three related logs, e.g. the Session which uniquely identifies the call.
Some fields I only want the first log's value, e.g. Date which may be a few seconds different in the second and third log.
Some fields are shared for the three different purposes, e.g. Parameters gives the Input Model for Call Begin, Output Model for Call Response, and HTTP response (e.g. OK) for Call End.
Some fields are unused for two of the purposes, e.g. ExecutionTime is -1 for Call Begin and Call Response, and a value in ms for Call End.
How can I "roll up" the sets of 3 rows into one row per set? I have tried using DISTINCT and GROUP BY, but the fact that some of the information collides is making it very difficult. I apologize that my SQL isn't really good enough to really explain what I'm asking for - so perhaps an example will make it clearer:
Example of what I have:
SQL:
SELECT * FROM [dbo].[Log]
Results:
+---------+---------------------+-------+------------+---------------+---------------+-----------------+--+
| Session | Date | Level | Context | Message | ExecutionTime | Parameters | |
+---------+---------------------+-------+------------+---------------+---------------+-----------------+--+
| 84248B7 | 2014-07-20 19:16:15 | INFO | GET v1/abc | Call Begin | -1 | {"Input":"xx"} | |
| 84248B7 | 2014-07-20 19:16:15 | INFO | GET v1/abc | Call Response | -1 | {"Output":"yy"} | |
| 84248B7 | 2014-07-20 19:16:15 | INFO | GET v1/abc | Call End | 123 | OK | |
| F76BCBB | 2014-07-20 19:16:17 | ERROR | GET v1/def | Call Begin | -1 | {"Input":"ww"} | |
| F76BCBB | 2014-07-20 19:16:18 | ERROR | GET v1/def | Call Response | -1 | {"Output":"vv"} | |
| F76BCBB | 2014-07-20 19:16:18 | ERROR | GET v1/def | Call End | 456 | BadRequest | |
+---------+---------------------+-------+------------+---------------+---------------+-----------------+--+
Example of what I want:
SQL:
[Need to write this query]
Results:
+---------------------+-------+------------+----------+---------------+----------------+-----------------+--------------+
| Date | Level | Context | Message | ExecutionTime | InputModel | OutputModel | HttpResponse |
+---------------------+-------+------------+----------+---------------+----------------+-----------------+--------------+
| 2014-07-20 19:16:15 | INFO | GET v1/abc | Api Call | 123 | {"Input":"xx"} | {"Output":"yy"} | OK |
| 2014-07-20 19:16:17 | ERROR | GET v1/def | Api Call | 456 | {"Input":"ww"} | {"Output":"vv"} | BadRequest |
+---------------------+-------+------------+----------+---------------+----------------+-----------------+--------------+

Answer 1

select L1.Session, L1.Date, L1.Level, L1.Context, 'Api Call' AS Message,
L3.ExecutionTime,
L1.Parameters as InputModel,
L2.Parameters as OutputModel,
L3.Parameters as HttpResponse
from Log L1
inner join Log L2 ON L1.Session = L2.Session
inner join Log L3 ON L1.Session = L3.Session
where L1.Message = 'Call Begin'
and L2.Message = 'Call Response'
and L3.Message = 'Call End'
This would work in your sample.