从表中选择前N行包含N的列

删除了facepalm后的第一个答案。

您的示例唯一的问题是在TOP查询中没有ORDER BY,这可能会以任何顺序提取结果。此查询假定您是按LineItemID(整数类型)ASC排序的。

DECLARE @LineItems TABLE
(
    LineItemID INT
    , PO INT
    , NumLineItems INT
)

INSERT INTO @LineItems (LineItemID, PO, NumLineItems)
SELECT 11111111,   12345,   3
UNION ALL SELECT 22222222,   12345,   3
UNION ALL SELECT 33333333,   12345,   3
UNION ALL SELECT 44444444,   12345,   3
UNION ALL SELECT 55555555,   12345,   3
UNION ALL SELECT 66666666,   12345,   3
UNION ALL SELECT 77777777,   54321,   2
UNION ALL SELECT 88888888,   54321,   2
UNION ALL SELECT 99999999,   54321,   2
UNION ALL SELECT 10101010,   54321,   2

DELETE b
FROM
(
    SELECT *
        , RANK() OVER (PARTITION BY PO, NumLineItems ORDER BY LineItemID ASC) AS r
    FROM @LineItems
) a
JOIN @LineItems b
    ON a.LineItemID = b.LineItemID
WHERE r > a.NumLineItems

SELECT *
FROM @LineItems
ORDER BY PO, LineItemID

delete t from (select *, rank = row_number() over (partition by PO# order by lineitemid) 
               from table ) t 
where rank > #lineitems