Create a reusable function to split Delimiter separated string into row 

CREATE FUNCTION [dbo].[Split](@String NVARCHAR(MAX), @Delimiter char(1)) 
returns @temptable TABLE (items NVARCHAR(MAX)) 
as 
begin 
declare @idx int 
declare @slice NVARCHAR(MAX) 

select @idx = 1 
if len(@String)<1 or @String is null return 

while @idx!= 0 
begin 
set @idx = charindex(@Delimiter,@String) 
if @idx!=0 
set @slice = left(@String,@idx - 1) 
else 
set @slice = @String 

if(len(@slice)>0)
insert into @temptable(Items) values(@slice) 

set @String = right(@String,len(@String) - @idx) 
if len(@String) = 0 break 
end 
return 
end

Test It

SELECT tb.a 
INTO #tmp
FROM
(SELECT '1,23,5' a
UNION ALL
SELECT '5,9,15' a) tb;

-------------------------------------------

SELECT * FROM #tmp;

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SELECT
items
FROM (SELECT a
FROM #tmp) tb
CROSS APPLY dbo.Split(tb.a, ',');