Unsure what SQL query is attempting to do - sql

Question

I am working on some inherited code, and am having an issue with an SQL Query within it. The query is as follows.
Select distinct
g.scriptid,
g.procedurename,
h.parameters,
g.scriptname,
h.usercode,
h.facility,
h.recid,
cast((cast(recid as varchar) + '.' + Right('0000' + cast(scriptgennum as varchar), 4)) as decimal(10,4)) as 'scriptrecid',
scriptgennum+1 as 'scriptgennum',
h.generated,
h.runinterval,
case
when runinterval = 'M' then dateadd(month,1,convert(varchar(10),h.nextrundate,120))
when runinterval = 'Q' then dateadd(month,3,convert(varchar(10),h.nextrundate,120))
when runinterval = 'W' then dateadd(week,1,convert(varchar(10),h.nextrundate,120))
when runinterval = '0' then NULL end as 'nextrundate',
convert(varchar(10),getdate(),120) as currentrundate,
scripttype
from PATIENTLETTERS_SCRIPTHIST h join PATIENTLETTERS_SCRIPTS g on
g.scriptid = h.scriptid where
h.status = 'Y'
and (([runinterval] = 'M'
and (convert(varchar(10),nextrundate,120) = convert(varchar(10),getdate(),120)
and datepart(day,getdate()) = 5
and (datediff(month,convert(varchar(10),h.lastrundate,120),convert(varchar(10),getdate(),120)) = 1)
or lastrundate is null))
or ([runinterval] = 'Q'
and (convert(varchar(10),nextrundate,120) = convert(varchar(10),getdate(),120)
and datepart(weekday,getdate()) = 0
and (datediff(month,convert(varchar(10),h.lastrundate,120),convert(varchar(10),getdate(),120)) = 3)
or lastrundate is null))
or ([runinterval] = 'W'
and (convert(varchar(10),nextrundate,120) = convert(varchar(10),getdate(),120)
and datepart(day,getdate()) = 5
and (datediff(week,convert(varchar(10),h.lastrundate,120),convert(varchar(10),getdate(),120)) = 1)
or lastrundate is null))
or ([runinterval] = 'O'
and (convert(varchar(10),nextrundate,120) = convert(varchar(10),getdate(),120)
and (datepart(weekday,getdate()) = 0))
or lastrundate is null))
I know that it is trying to select the specific columns listed from PATIENTLETTERS_SCRIPTHIST and PATIENTLETTERS_SCRIPTS. The part of the query that has me confused are the lines like these:
and (([runinterval] = 'M'
and (convert(varchar(10),nextrundate,120) = convert(varchar(10),getdate(),120)
and datepart(day,getdate()) = 5
and (datediff(month,convert(varchar(10),h.lastrundate,120),convert(varchar(10),getdate(),120)) = 1)
If someone can explain what those lines are actually doing I would greatly appreciate any help. I can see that it wants to make sure that the run interval is 'M', and it looks like its trying to match up the current date to the day in stored in the database in the 4th line, but the 2nd and 3rd lines are still a complete mystery.

Answer 1

Looking for items set to run monthly, where the next run date is today, and today is the 5th of the month, and it's been exactly one month since the item was last run.
More info on CONVERT
and DATEPART

Answer 2

This code is looking for items that have a runinterval = 'M'
line 1 - [runinterval] = 'M'
and the nextrundate is equal to the current date (getdate()), the dates are being converted to a varchar with the same formatting.
line 2 - and (convert(varchar(10),nextrundate,120) = convert(varchar(10),getdate(),120)
and the current date has a day equal to 5. Meaning that the date would have to be June 5, July 5, etc
line 3 - and datepart(day,getdate()) = 5
and the difference between the month of the lastrundate and the current date (getdate()) is equal to 1
line 4 - (datediff(month,convert(varchar(10),h.lastrundate,120),convert(varchar(10),getdate(),120)) = 1)

Answer 3

The second line converts nextrundate and the current date to 'YYYY-MM-DD' format using style 120 (More details here) then checks that they're the same, so only rows where nextrundate is today.
The third line just checks that today is the 5th day of the month. For instance:
SELECT DATEPART(DAY, '2012-07-05') returns 5.