Kapan menggunakan operator tabel BERLAKU

Pertama-tama - dengan apply Anda dapat memanggil fungsi bernilai tabel di mana nilai parameter diambil dari tabel yang Anda kueri, seperti ini:

select
    t1.col3, -- column from table
    f1.col1  -- column from function
from table1 as t1
    left outer join table2 as t2 on t2.col1 = t1.col1
    outer apply dbo.function1(t1.col1, t2.col2) as f1

atau menghancurkan kolom xml

select
    t1.col3,
    t.c.value('@value', 'int') as value
from table1 as t1
    -- table1.col1 is xml iike <Data @Value="...">...</Data>
    outer apply t1.col1.nodes('Data') as t(c) 

Dari pengalaman saya, apply sangat berguna ketika Anda harus membuat beberapa pra-perhitungan :

select
    t1.col3,
    a1.col1,  --calculated value
    a2.col1   -- another calculated value, first one was used
from table1 as t1
    outer apply (select t1.col1 * 5 as col1) as a1
    outer apply (select a1.col1 - 4 as col1) as a2

contoh lain dari penggunaan apply adalah tidak berputar operasi:

select
    t1.col1, c.name, c.value
from table1 as t1
    outer apply (
        select 'col1', t1.col1 union all
        select 'col2', t1.col2
    ) as c(name, value)

akhirnya, inilah permintaan Anda diimplementasikan dalam SQL 2005 tanpa menggunakan apply :

;with cte as (
    select
        y.Name, 
        y.hoursWorked,
        x.game,
        x.NumBets,
        row_number() over(partition by x.Name order by x.NumBets) as row_num
    from y
        left outer join x on x.Name = y.Name
)
select Name, hoursWorked, game, NumBets
from cte
where row_num <= 2
order by Name, NumBets desc

lihat sql fiddle contoh