Anda membutuhkan CROSS APPLY di sini, ini dapat merujuk ke referensi luar, tidak diperlukan subquery atau CTE yang mengganggu:
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
Beberapa trik lagi yang dapat Anda lakukan dengan APPLY :
1. 1 teratas per grup tabel anak:
Solusi klasik untuk "1 teratas per grup" adalah dengan menggunakan row_number() . Ini sering kali dapat menghasilkan pemindaian yang besar, terutama bila jumlah nilai luar yang berbeda relatif kecil dibandingkan tabel anak.
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
Sebagai gantinya kita dapat melakukan:
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
Catatan:OUTER APPLY secara konseptual menggantikan gabungan kiri, yaitu mengembalikan nol alih-alih tanpa baris.
2. Membatalkan putaran
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)
3. Meledak satu baris beberapa kali variabel:
Katakanlah kita ingin mengambil jumlah, dan membaginya menjadi beberapa baris. Jika amount <= 50 lalu satu baris amount , jika > 50 lalu dua baris, satu dari 50 dan satu lagi:
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
