evaluation with condition

[zacksoft]

I have two values x and y. Both values are dynamic (keeps on changing).
x indicates _time and y indicates a value that continuosly changes with time.
I want the value of y at two particular instances of x.

I do this,
|eval mytime = round(_time)
|eval mytime2 = round(_time) - 40

I wish to have value of y when x's value is mytime and
the value of y when x's value is mytime2 (i.e. 40 sec before current time)
If condition only helps to get the value of y when x is mytime, but it won't help when x = mytime2. When x=mytime2 , it still gives the same value as mytime. But it shouldn't be the case.

[493669]

could you provide what query you have tried?

[493669]

could you provide sample inputs and expected output to better understand

[zacksoft]

X | Y
1518074558| 464758
1518074559| 5757657
1518074560| 464533
1518074561| 667231
1518074562| 77654
1518074563| 00987
1518074564 | 567843

X indicates UNIX time.