Weird Interleaving requirement - sql

Question

I have a log table that contains (to be simple), user, operation, date.
There are two operations: search and view (search may return a hundred records; the user may view zero or more).
I need to have the basic output sorted by date, but I also need to have all of the views for one search together. Something like
name operation date
john search 1/1 1pm
john view 1/1 2pm
john view 1/1 3pm
james search 1/1 230pm
james view 1/1 315pm
john search 1/1 310pm
It seems I need to use the results of a subquery to perform the query, but I'm not sure how that would look. I'm OK with SQL but I kind of hit the ceiling with JOINs and UNIONs. :-/

Answer 1

You can identify the groups by using a window function. And you can include the window function in the order by, so no subqueries are needed.
select *
from log_table l
order by max(case when l.operation = 'search' then l.log_date end) over (partition by l.name order by l.log_date),
l.name,
l.log_date;
Here is a db<>fiddle.

Answer 2

You can use a conditional lag() call to find the most recent search date/time for each view row, per user; with search rows getting their own date/time:
-- CTE for sample data
with log_table (name, operation, log_date) as (
select 'john', 'search', timestamp '2019-01-01 13:00:00' from dual
union all select 'john', 'view', timestamp '2019-01-01 14:00:00' from dual
union all select 'john', 'view', timestamp '2019-01-01 15:00:00' from dual
union all select 'james', 'search', timestamp '2019-01-01 14:30:00' from dual
union all select 'james', 'view', timestamp '2019-01-01 15:15:00' from dual
union all select 'john', 'search', timestamp '2019-01-01 15:10:00' from dual
)
-- actual query
select name, operation, log_date,
case when operation = 'search' then log_date
else lag(case when operation = 'search' then log_date end ignore nulls)
over (partition by name order by log_date)
end as search_date
from log_table
order by log_date;
NAME OPERATION LOG_DATE SEARCH_DATE
----- --------- ------------------- -------------------
john search 2019-01-01 13:00:00 2019-01-01 13:00:00
john view 2019-01-01 14:00:00 2019-01-01 13:00:00
james search 2019-01-01 14:30:00 2019-01-01 14:30:00
john view 2019-01-01 15:00:00 2019-01-01 13:00:00
john search 2019-01-01 15:10:00 2019-01-01 15:10:00
james view 2019-01-01 15:15:00 2019-01-01 14:30:00
You can then use that as a CTE or inline view, and use the generated search_date to order first, then order the records with the same search date by their actual log date:
-- CTE for sample data
with log_table (name, operation, log_date) as (
select 'john', 'search', timestamp '2019-01-01 13:00:00' from dual
union all select 'john', 'view', timestamp '2019-01-01 14:00:00' from dual
union all select 'john', 'view', timestamp '2019-01-01 15:00:00' from dual
union all select 'james', 'search', timestamp '2019-01-01 14:30:00' from dual
union all select 'james', 'view', timestamp '2019-01-01 15:15:00' from dual
union all select 'john', 'search', timestamp '2019-01-01 15:10:00' from dual
)
-- actual query
select name, operation, log_date
from (
select name, operation, log_date,
case when operation = 'search' then log_date
else lag(case when operation = 'search' then log_date end ignore nulls)
over (partition by name order by log_date)
end as search_date
from log_table
)
order by search_date, log_date;
NAME OPERATION LOG_DATE
----- --------- -------------------
john search 2019-01-01 13:00:00
john view 2019-01-01 14:00:00
john view 2019-01-01 15:00:00
james search 2019-01-01 14:30:00
james view 2019-01-01 15:15:00
john search 2019-01-01 15:10:00
As you could potentially get simultaneous searches from two users, you might want to include the user in the final order-by clause too:
...
order by search_date, name, log_date;