SQL query, select values of a column only if

Question

Im using SLQ server 2005.

I have this table were i register a list of items creating an "order" wich will be sent to the warehouse so they know what it needs to be sent back.

this is my code.

id_pedido=id_order, id_articulo=id_item, descripcion=description, fecha=date, nombre=employee name, local=store, (inicia+entra+sale) Existencias=stocks, tipo=Kind, --estado=state, activo=active.--

select id, id_pedido, p.id_articulo, p.descripcion, p.fecha, u.nombre, p.local,a.inicia+a.entra-a.sale as Existencias, a.tipo
from pedidos p join usuarios u on p.id_usuario=u.id_usuario join articulos a on a.id_articulo=p.id_articulo
where estado='activo'

What i need is that in stocks column values ​​are displayed only when the kind of the item is X. How can i show all rows with null in the stocks column when their kind is not X and the value when the kind is X?

This is because the client only want the employee to know the stock of those items but not of all the others.

Answer 1

You can use CASE to compare the the tipo column to the value needed:

select id, 
   id_pedido, 
   p.id_articulo, 
   p.descripcion, 
   p.fecha, 
   u.nombre, 
   p.local,
   case when a.tipo = 'X' then a.inicia+a.entra-a.sale end Existencias, 
   a.tipo
from pedidos p 
   join usuarios u on p.id_usuario=u.id_usuario 
   join articulos a on a.id_articulo=p.id_articulo
where estado='activo'