sql - setting alias on mysql columns with math operators -

this sql query getting error @ statement.

select a.*, b.*, (a.date - b.date) before tbl a join tbl b b on a.id = b.id (a.date - b.date) < 5 , (a.date - b.date)  > 0; 

how can make sql query , working?

select a.*, b.*, (a.date - b.date) before tbl a join tbl b b on a.id = b.id before < 5 , before > 0; 

before reserved word. use else or use backticks:

select a.*, b.*, (a.date - b.date) datediff tbl a join      tbl b b      on a.id = b.id (a.date - b.date) < 5 , (a.date - b.date)  > 0; 

the list of reserved words here. before used in definition of triggers (and perhaps other places).

edit:

for second question, can use having clause if want:

select a.*, b.*, (a.date - b.date) datediff tbl a join      tbl b b      on a.id = b.id having datediff < 5 , datediff > 0; 

this mysql extension having. looks awkward not familiar (it screaming, "where group by"). but, can useful, particularly longer, more complicated expressions.