Retrieve data 60 days prior to their retest date - sql

Question

I have a requirement where I need to retrieve Row(s) 60 days prior to their "Retest Date" which is a column present in the table. I have also attached the screenshot and the field "Retest Date" is highlighted.
reagentlotid
reagentlotdesc
u_retest
RL-0000004
NULL
2021-09-30 17:00:00.00
RL-0000005
NULL
2021-09-29 04:21:00.00
RL-0000006
NULL
2021-09-29 04:22:00.00
RL-0000007
Y-T4
2021-08-28 05:56:00.00
RL-0000008
NULL
2021-09-30 05:56:00.00
RL-0000009
NULL
2021-09-28 04:23:00.00
This is what I was trying to do in SQL Server:
select r.reagentlotid, r.reagentlotdesc, r.u_retestdt
from reagentlot r
where u_retestdt = DATEADD(DD,60,GETDATE());
But, it didn't work. The above query returning 0 rows.
Could please someone help me with this query?

Answer 1

Use a range, if you want all data from the day 60 days hence:
select r.reagentlotid, r.reagentlotdesc, r.u_retestdt
from reagentlot r
where
u_retestdt >= CAST(DATEADD(DD,60,GETDATE())
AS DATE) AND
u_retestdt < CAST(DATEADD(DD,61,GETDATE()) AS DATE)
Dates are like numbers; the time is like a decimal part. 12:00:00 is half way through a day so it's like x.5 - SQLServer even lets you manipulate datetime types by adding fractions of days etc (adding 0.5 is adding 12h)
If you had a column of numbers like 1.1, 1.5. 2.4 and you want all the one-point-somethings you can't get any of them by saying score = 1; you say score >= 1 and score < 2
Generally, you should try to avoid manipulating table data in a query's WHERE clause because it usually makes indexes unusable: if you want "all numbers between 1 and 2", use a range; don't chop the decimal off the table data in order to compare it to 1. Same with dates; don't chop the time off - use a range:
--yes
WHERE score >= 1 and score < 2
--no
WHERE CAST(score as INTEGER) = 1
--yes
WHERE birthdatetime >= '1970-01-01' and birthdatetime < '1970-01-02'
--no
WHERE CAST(birthdatetime as DATE) = '1970-01-01'
Note that I am using a CAST to cut the time off in my recommendation to you, but that's to establish a pair of constants of "midnight on the day 60 days in the future" and "midnight on 61 days in the future" that will be used in the range check.
Follow the rule of thumb of "avoid calling functions on columns in a where clause" and generally, you'll be fine :)

Answer 2

Try something like this. -60 days may be the current or previous year. HTH
;with doy1 as (
select DATENAME(dayofyear, dateadd(day,-60,GetDate())) as doy
)
, doy2 as (
select case when doy > 0 then doy
when doy < 0 then 365 - doy end as doy
, case when doy > 0 then year(getdate())
when doy < 0 then year(getdate())-1 end as yr
from doy1
)
select r.reagentlotid
, r.reagentlotdesc
, cast(r.u_retestdt as date) as u_retestdt
from reagentlot r
inner join doy2 d on DATENAME(dayofyear, r.u_retestdt) = d.doy
where DATENAME(dayofyear, r.u_retestdt) = doy
and year(r.u_retestdt) = d.yr