Question

I have a master table like

CityName, Month, Temperature

A,Jan,20
….
A,Dec,1
B,Jan,30
….
Z,December,12

I would like to generate a differentiation table like

iCity,jCity,Month,DifferentTemperature
A, B, Jan, a.temperature-b.temperature
…
A, Z, Dec, a. temperature-z.temperature
…..

each row would loop through the rest row on a particular month in the master table.

What is the best way to do that? How did you come up an idea to solve this problem?

Thank you very much!

Answer 1

Sounds like you’re looking for a CROSS APPLY Something like

SELECT
    M1.city AS iCity
,   M2.city AS jCity
,   M1.month
,   M1.temperature - M2.temperature AS final_temperature
FROM
    MASTER M1
    CROSS APPLY
    MASTER M2
    ON M2.month = M1.month