How Do you add/substract from previous row in SQL?

In Mysql

Table

Id AA BBB 
A  45 123
B  52 120
C  40 135

How would I get

B_A  7 
A_C  5

First would need to sort by BBB Asc then minus 52-45. B_A concatenate B and A

How Do you add/substract form previous row in SQL?

If I needed to ha开发者_运维百科ve seperate cols for B then A, How Would I add this.

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SELECT concat(t1.id , '_',  t2.id, ' ', t1.aa - t2.aa ) 
FROM   table t1 
       INNER JOIN (SELECT Max(t2.id) prev_id, 
                          t1.id 
                   FROM   table t1 
                          INNER JOIN table t2 
                            ON t1.id > t2.id
                   GROUP BY t1.id) prev 
         ON t1.id = prev.id 
       INNER JOIN table t2 
         ON t2.id = prev.prev_id