sql server - Simplify SQL Query using variable -

i want simplfy t-sql query. :

select      t.a [column a],      t.b [column b],     t.c [column c],     (t.a - t.b - t.c) [column d],     case       when (t.a - t.b - t.c) = 0 'equals'       when (t.a - t.b - t.c) > 0 'greater'       when (t.a - t.b - t.c) < 0 'less'     end [status]                table1 t; 

it nice put (t.a - t.b - t.c) variable, can reuse on places occurs, because expression may change on time. not figure out how without changing existing query significantly.

use cross apply

select     t.a [column a],      t.b [column b],     t.c [column c],     [column d],     case       when [column d] = 0 'equals'       when [column d] > 0 'greater'       when [column d] < 0 'less'     end [status]                table1 t     cross apply (select t.a - t.b - t.c [column d]) t2