Exclude rows where dates exist in another table - sql

Question

I have 2 tables, one is working pattern, another is absences.
1) Work pattern
ID | Shift Start | Shift End
123| 01-03-2017 | 02-03-2017
2) Absences
ID| Absence Start | Absence End
123| 01-03-2017 | 04-03-2017
What would be the best way, when selecting rows from work pattern, to exclude any that have a date marked as an absence in the absence table?
For example, I have a report that uses the work pattern table to count how may days a week an employee has worked, however I don't want it to include the days that have been marked as an absence on the absence table if that makes sense? Also don't want it to include any days that fall between the absence start and absence end date?

Answer 1

If the span of the absence should always encompass the shift to be excluded you can use not exists():
select *
from WorkPatterns w
where not exists (
select 1
from Absences a
where a.Id = w.Id
and a.AbsenceStart <= w.ShiftStart
and a.AbsenceEnd >= w.ShiftEnd
)
rextester demo: http://rextester.com/DCODC76816
returns:
+-----+------------+------------+
| id | ShiftStart | ShiftEnd |
+-----+------------+------------+
| 123 | 2017-02-27 | 2017-02-28 |
| 123 | 2017-03-05 | 2017-03-06 |
+-----+------------+------------+
given this test setup:
create table WorkPatterns ([id] int, [ShiftStart] datetime, [ShiftEnd] datetime) ;
insert into WorkPatterns ([id], [ShiftStart], [ShiftEnd]) values
(123, '20170227', '20170228')
,(123, '20170301', '20170302')
,(123, '20170303', '20170304')
,(123, '20170305', '20170306')
;
create table Absences ([id] int, [AbsenceStart] datetime, [AbsenceEnd] datetime) ;
insert into Absences ([id], [AbsenceStart], [AbsenceEnd]) values
(123, '20170301', '20170304');

Answer 2

What would be the best way, when selecting rows from work pattern
If you dealing only whit dates (no time) and have control over db schema,
One approach will be to create calendar table ,
Where you going to put all dates since company started and some years in future
Fill that table once.
After it is easy to join other tables whit dates and do math.
If you have trouble whit constructing TSQL query please edit question whit more details about columns and values of tables, relations and needed results.

Answer 3

How about this:
SELECT WP_START.[id], WP_START.[shift_start], WP_START.[shift_end]
FROM work_pattern AS WP_START
INNER JOIN absences AS A ON WP_START.id = A.id
WHERE WP_START.[shift_start] NOT BETWEEN A.[absence_start] AND A.[absence_end]
UNION
SELECT WP_END.[id], WP_END.[shift_start], WP_END.[shift_end]
FROM work_pattern AS WP_END
INNER JOIN absences AS A ON WP_END.id = A.id
WHERE WP_END.[shift_end] NOT BETWEEN A.[absence_start] AND A.[absence_end]
See it on SQL Fiddle: http://sqlfiddle.com/#!6/49ae6/6

Answer 4

Here is my example that includes a Date Dimension table. If your DBAs won't add it, you can create #dateDim as a temp table, like I've done with SQLFiddle (didn't know I could do that). A typical date dimension would have a lot more details you need about the days, but if the table can't be added, just use what you need. You'll have to populate the other Holidays you need. The DateDim I use often is at https://github.com/shawnoden/SQL_Stuff/blob/master/sql_CreateDateDimension.sql
SQL Fiddle
MS SQL Server 2014 Schema Setup:
/* Tables for your test data. */
CREATE TABLE WorkPatterns ( id int, ShiftStart date, ShiftEnd date ) ;
INSERT INTO WorkPatterns ( id, ShiftStart, ShiftEnd )
VALUES
(123, '20170101', '20171031')
, (124, '20170601', '20170831')
;
CREATE TABLE Absences ( id int, AbsenceStart date, AbsenceEnd date ) ;
INSERT INTO Absences ( id, AbsenceStart, AbsenceEnd )
VALUES
( 123, '20170123', '20170127' )
, ( 123, '20170710', '20170831' )
, ( 124, '20170801', '20170820' )
;
/* ******** MAKE SIMPLE CALENDAR TABLE ******** */
CREATE TABLE dateDim (
theDate DATE NOT NULL
, IsWeekend BIT DEFAULT 0
, IsHoliday BIT DEFAULT 0
, IsWorkDay BIT DEFAULT 0
);
/* Populate basic details of dates. */
INSERT dateDim(theDate, IsWeekend, IsHoliday)
SELECT d
, CONVERT(BIT, CASE WHEN DATEPART(dw,d) IN (1,7) THEN 1 ELSE 0 END)
, CONVERT(BIT, CASE WHEN d = '20170704' THEN 1 ELSE 0 END) /* 4th of July. */
FROM (
SELECT d = DATEADD(DAY, rn - 1, '20170101')
FROM
(
SELECT TOP (DATEDIFF(DAY, '20170101', '20171231'))
rn = ROW_NUMBER() OVER (ORDER BY s1.[object_id])
FROM sys.all_objects AS s1
CROSS JOIN sys.all_objects AS s2
ORDER BY s1.[object_id]
) AS x
) AS y ;
/* If not a weekend or holiday, it's a WorkDay. */
UPDATE dateDim
SET IsWorkDay = CASE WHEN IsWeekend = 0 AND IsHoliday = 0 THEN 1 ELSE 0 END
;
Query For Calculation:
SELECT wp.ID, COUNT(d.theDate) AS workDayCount
FROM WorkPatterns wp
INNER JOIN dateDim d ON d.theDate BETWEEN wp.ShiftStart AND wp.ShiftEnd
AND d.IsWorkDay = 1
LEFT OUTER JOIN Absences a ON d.theDate BETWEEN a.AbsenceStart AND a.AbsenceEnd
AND wp.ID = a.ID
WHERE a.ID IS NULL
GROUP BY wp.ID
ORDER BY wp.ID
Results:
| ID | workDayCount |
|-----|--------------|
| 123 | 172 | << 216 total days, 44 non-working
| 124 | 51 | << 65 total days, 14 non-working