Necesitas CROSS APPLY
aquí, puede referirse a referencias externas, no se necesitan subconsultas molestas o CTE:
select col1, col2
from table1 as outer_table
-- can also have multi-row values
cross apply (values (complex_expression_1) ) as v1 (col1)
cross apply (values (expression_referring_to_col1) ) as v2 (col2)
-- alternate syntax, select without from returns a single row
cross apply (select complex_expression_1 as col1 ) AS v1
cross apply (select expression_referring_to_col1 as col2 ) as v2
-- you can also do anything you like in there, can be one or multiple rows
cross apply (
select complex_expression_1 as col1
from othercomplexjoin as o
where o.join_column = outer_table.join_column
) AS v1
Algunos trucos más que puedes hacer con APPLY
:
Una solución clásica para el "top 1 por grupo" es usar row_number()
. Esto a menudo puede resultar en escaneos enormes, especialmente cuando la cantidad de valores externos distintos es pequeña en relación con la tabla secundaria.
select
o.id,
lastPayment.Date
from order_header as o
join
( select *, row_number() over (partition by order_id order by date desc) as rn
from payments
) as lastPayment on ...
where lastPayment.rn = 1
En su lugar, podemos hacer:
select
o.id,
lastPayment.Date
from order_header as o
cross apply
( select top (1) *
from payments as p
where p.order_id = o.id
order by date desc
) as lastPayment
Nota:OUTER APPLY
reemplaza conceptualmente una combinación izquierda, es decir, devuelve valores nulos en lugar de ninguna fila.
select
o.id,
customer.*
from order_header as o
cross apply ( values -- This returns two rows for every order_header
( 'DeliveryCustomer', o.deliveryCustomer ),
( 'billingCustomer', o.billingCustomer )
) as customer (type, name)
Digamos que queremos tomar una cantidad y dividirla en diferentes filas. Si el amount <= 50
luego una fila de amount
, si > 50
luego dos filas, una de 50 y otra del resto:
select t.id, v.amount
from table as t
cross apply (
select case when amount > 50 then 50 else amount end as amount
union all
select amount - 50 -- note this row will not appear if amount < 50
where amount > 50
) v