SQL - Operand data type datetime2 is invalid for subtract operator

Question

I want to subtract the value of the first row from the value of the second row of column _timestamp (shown below). _number is the ordering column i

Answer 1

As mentioned in the comments, you can't subtract timestamps with - operator. Use DATEDIFF function instead. To get the difference of the current row and the next row's timestamps, use OUTER APPLY.

select t2._number,t2._timestamp, 
datediff(microsecond,t2._timestamp,t1._timestamp) as diff
from dbo.tbl t2
outer apply (select t1._timestamp 
             from dbo.tcp t1
             where t1._number = t2._number + 1) t1

Edit: To update a column named diff per the OP's comment,

with cte as (          
select t2._number,t2._timestamp, t2.diff,
datediff(microsecond,t2._timestamp,t1._timestamp) as diff_col
from t t2
outer apply (select t1._timestamp 
             from t t1
             where t1._number = t2._number + 1) t1
   )
update cte set diff=diff_col;