How to write a SQL function into Acces 2003 -

so have acces table : data

data made of :

• client id
• product id
• sell category ( exemple : sell dones, sell planed ,forecast sales) ,written in letters
• quantity sold .
• unitary price.

i trying build single acces query display things :

|client id||product id||total sell dones||total sell planed||total forecast sell||quantity sell dones||quantity sell planed||quantity forecast| 

how can ?

like if had 1 type of sell , 1 single quantity :

select (sells*quantity) [total sells] 

but thing here have different quantity , different types of sells put if select ?

something :

select (if data.sell category="planned sell" quantity sold*unitary price else 0) [total planned sell] , etc etc (for every single 1 ? 

the thing using acces 2003 , dont think can create sql function in acces 2003 , use in select , if can willing , else if can use "select,delete,update " in acces 2003 guess have this