SQL - Conditional column selection in join - sql

Question

I am not sure if this scenario can be achieved using TSQL. I have a table called WorkingDays, which have this info
ID | EmployeeId | Monday | Tuesday | Wednesday | Thursday | Friday
----------------------------------------------------------------------
1 | 1 | 2 | 2 | 3 | 6 | 5
2 | 2 | 1 | 7 | 5 | 2 | 3
The days columns store Ids of WorkingSchedule table, which has this columns:
ID int Primary Key
StartTime time
EndTime time
So what I need id get the StartTime and EndTime of an employee depending on the current date.
What I need to get from query is the start and end time depending on the day. The day I want to filter is de current date (using getdate() function)
So need to select the correct day column name to make the join.
How can I achieve this scenario?

Answer 1

The dynamic sql version:
declare #sql nvarchar(max) ='
select
t.EmployeeId
, StarTime = max(case when t.rn=1 then '+quotename(datename(weekday,getdate()))+' end)
, EndTime = max(case when t.rn=2 then '+quotename(datename(weekday,getdate()))+' end)
from (
select *
, rn = row_number() over (partition by t.EmployeeId order by t.Id)
from t
) t
group by t.EmployeeId;'
exec sp_executesql #sql;
rextester demo: http://rextester.com/WNH34961
returns:
+------------+----------+---------+
| EmployeeId | StarTime | EndTime |
+------------+----------+---------+
| 1 | 5 | 3 |
+------------+----------+---------+
Depending on how you want the output, here are two other ways that do not use dynamic sql:
Both use cross apply() to unpivot the data, and WorkDay = datename(weekday,getdate()) to get the current WorkDay column.
For one row output we add some conditional aggregation:
/* one row per employeeId */
select
t.EmployeeId
, x.WorkDay
, StarTime = max(case when t.rn=1 then x.Time end)
, EndTime = max(case when t.rn=2 then x.Time end)
from (
select *
, rn = row_number() over (partition by t.EmployeeId order by t.Id)
from t
) t
cross apply (values
('Monday',Monday),('Tuesday',Tuesday),('Wednesday',Wednesday)
,('Thursday',Thursday),('Friday',Friday)
) x (WorkDay,Time)
where WorkDay = datename(weekday,getdate())
group by t.EmployeeId, x.WorkDay
returns:
+------------+---------+----------+---------+
| EmployeeId | WorkDay | StarTime | EndTime |
+------------+---------+----------+---------+
| 1 | Friday | 5 | 3 |
+------------+---------+----------+---------+
If you want the output on two rows, like your current output:
/* two rows per employeeId */
select
t.Id
, t.EmployeeId
, x.WorkDay
, t.StartEnd
, x.Time
from (
select *
, StartEnd = case
when row_number() over (partition by t.EmployeeId order by t.Id) = 1
then 'StartTime'
else 'EndTime'
end
from t
) t
cross apply (values
('Monday',Monday),('Tuesday',Tuesday),('Wednesday',Wednesday)
,('Thursday',Thursday),('Friday',Friday)
) x (WorkDay,Time)
where WorkDay = datename(weekday,getdate());
returns:
+----+------------+---------+-----------+------+
| Id | EmployeeId | WorkDay | StartEnd | Time |
+----+------------+---------+-----------+------+
| 1 | 1 | Friday | StartTime | 5 |
| 2 | 1 | Friday | EndTime | 3 |
+----+------------+---------+-----------+------+

Answer 2

select wd.Employee, ws.StartTime, ws.EndTime
from WorkingDays wd
join WorkingSchedule ws on ws.Id = case datename(weekday, getdate())
when 'Monday' then ws.Monday
when 'Tuesday' then ws.Tuesday
when 'Wednesday' then ws.Wednesday
when 'Thursday' then ws.Thursday
when 'Friday' then ws.Friday
else 0
end
Hint: datename(weekday, getdate()) returns you the weekday name in your current locale! This might be better:
select wd.Employee, ws.StartTime, ws.EndTime
from WorkingDays wd
join WorkingSchedule ws on ws.Id = case datepart(weekday, getdate())
when 1 then wd.Monday
when 2 then wd.Tuesday
when 3 then wd.Wednesday
when 4 then wd.Thursday
when 5 then wd.Friday
else 0
end
But then you have to check which day is the first of week (0, 1), depending on your settings.