Use something like LEAST in T-SQL on a datetime field [duplicate] - sql

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Getting the minimum of two values in sql
Okay what I Have a table with two datetime fields and I want to select the rows where the oldest date is equal to some date variable. I saw the LEAST function used somewhere but I can't use this in T-SQL
I need something like this
SELECT LEAST(date1, date2) as theDate FROM theTable WHERE theDate = '2012-09-24'
but that will work in T-SQL. Also date1 or date2 can sometimes be null so that may be important to know.

Answer 1

The CASE solution others have provided works well for the case (no pun intended) of two values. For future reference, it becomes a bit unweildy for three or more values and you might then want to do something like this:
SELECT (SELECT MIN(mydate)
FROM (VALUES(date1),(date2),(date3)) mylist(mydate)
) AS theDate
FROM theTable
WHERE theDate = '2012-09-24'

Answer 2

There is no such function in T-SQL. Try:
SELECT theDate = CASE WHEN date1 < date2 THEN date1 ELSE date2 END FROM ... ;
To handle NULLs you may want:
SELECT theDate = NULLIF(CASE WHEN date1 < date2 THEN date1 ELSE date2 END, '20301231')
FROM
(
SELECT
date1 = COALESCE(date1, '20301231'),
date2 = COALESCE(date2, '20301231')
FROM ...
) AS x;
Also, you can't reference the alias theDate in the WHERE clause, it doesn't exist yet. You might want to say:
WHERE '20120924' IN (date1, date2);

Answer 3

You could use a case to mimic least, and a subquery so you can refer to the case result in the where clause:
select *
from (
select case
when date1 > date2 or date1 is null then date2
else date1
end as theDate
, *
from TheTable
)
where theDate = '2012-09-24'

Answer 4

While the other answers are indeed valid, here it is in the form of a UDF, which is closer to what you asked for:
CREATE FUNCTION [dbo].[LeastDate] (#d1 datetime, #d2 datetime)
RETURNS datetime
AS
BEGIN
DECLARE #least datetime
IF #d1 is null or #d2 is null
SET #least = null
ELSE IF #d1 < #d2
SET #least = #d1
ELSE
SET #least = #d2
RETURN #least
END
Usage:
SELECT dbo.LeastDate(date1, date2) as theDate
FROM theTable
WHERE dbo.LeastDate(date1, date2) = '2012-09-24'
Or you can use a nested select to do it one time only:
SELECT * FROM (
SELECT dbo.LeastDate(date1, date2) as theDate FROM theTable
) t
WHERE theDate = '2012-09-24'
Note that the choice of calling the function separately in the where clause or using a nested select is the same as it would be for any SQL function, not just this one.