只使用t-sql加入“最新”记录

Question

我有两张桌子。表“B”与表“A”具有一对多的关系，这意味着表“B”中的表“A”中的一条记录将有许多记录。

表“B”中的记录主要由日期区分，我需要生成一个结果集，其中包含表“A”中的记录，仅与表“B”中的最新记录相连。为了便于说明，这是一个示例模式：

Table A
-------
ID

Table B
-------
ID
TableAID
RowDate

我无法制定查询给我结果集我正在寻找任何帮助将不胜感激。

Answer 1

select a.*, bm.MaxRowDate
from (
    select TableAID, max(RowDate) as MaxRowDate
    from TableB
    group by TableAID
) bm
inner join TableA a on bm.TableAID = a.ID

如果您需要TableB中的更多列，请执行以下操作：

select a.*, b.* --use explicit columns rather than * here
from (
    select TableAID, max(RowDate) as MaxRowDate
    from TableB
    group by TableAID
) bm
inner join TableB b on bm.TableAID = b.TableAID
    and bm.MaxRowDate = b.RowDate
inner join TableA a on bm.TableAID = a.ID

Answer 2

SELECT *
FROM tableA A
OUTER APPLY (SELECT TOP 1 * 
             FROM tableB B
             WHERE A.ID = B.TableAID
             ORDER BY B.RowDate DESC) as B

Answer 3

With ABDateMap AS (
    SELECT Max(RowDate) AS LastDate, TableAID FROM TableB GROUP BY TableAID
),
LatestBRow As (
    SELECT MAX(ID) AS ID, TableAID FROM ABDateMap INNER JOIN TableB ON b.TableAID=a.ID AND b.RowDate = LastDate GROUP BY TableAID
)
SELECT columns
FROM TableA a
INNER JOIN LatestBRow m ON m.TableAID=a.ID
INNER JOIN TableB b on b.ID = m.ID

Answer 4

表B连接是可选的：它取决于您是否还有其他列

SELECT
    *
FROM
    tableA A
    JOIN
    tableB B ON A.ID = B.TableAID
    JOIN
    (
    SELECT Max(RowDate) AS MaxRowDate, TableAID
    FROM tableB
    GROUP BY TableAID
    ) foo ON B.TableAID = foo.TableAID AND B.RowDate= foo.MaxRowDate

Answer 5

只是为了清楚起见，并使那些偶然发现这个古老问题的人受益。如果在RowDate中有重复的Table B，则接受的答案将返回重复的行。更安全，更有效的方法是使用ROW_NUMBER()：

Select a.*, b.* -- Use explicit column list rather than * here
From [Table A] a
Inner Join ( -- Use Left Join if the records missing from Table B are still required
    Select *,
        ROW_NUMBER() OVER (PARTITION BY TableAID ORDER BY RowDate DESC) As _RowNum
    From [Table B]
) b
On b.TableAID = a.ID
Where b._RowNum = 1

Answer 6

试试这个：

    BEGIN

DECLARE @TB1 AS TABLE (ID INT, NAME VARCHAR(30) )
DECLARE @TB2 AS TABLE (ID INT, ID_TB1 INT, PRICE DECIMAL(18,2))

INSERT INTO @TB1 (ID, NAME) VALUES (1, 'PRODUCT X')
INSERT INTO @TB1 (ID, NAME) VALUES (2, 'PRODUCT Y')

INSERT INTO @TB2 (ID, ID_TB1, PRICE) VALUES (1, 1, 3.99)
INSERT INTO @TB2 (ID, ID_TB1, PRICE) VALUES (2, 1, 4.99)
INSERT INTO @TB2 (ID, ID_TB1, PRICE) VALUES (3, 1, 5.99)

INSERT INTO @TB2 (ID, ID_TB1, PRICE) VALUES (1, 2, 0.99)
INSERT INTO @TB2 (ID, ID_TB1, PRICE) VALUES (2, 2, 1.99)
INSERT INTO @TB2 (ID, ID_TB1, PRICE) VALUES (3, 2, 2.99)


SELECT A.ID, A.NAME, B.PRICE
  FROM @TB1 A
  INNER JOIN @TB2 B ON A.ID = B.ID_TB1 AND B.ID = (SELECT MAX(ID) FROM @TB2 WHERE ID_TB1 = A.ID)


END

Answer 7

这将使用JOIN获取最新记录。我认为这会对某人有所帮助

SELECT cmp.*, lr_entry.lr_no FROM 
(SELECT * FROM lr_entry ORDER BY id DESC LIMIT 1) 
lr_entry JOIN companies as cmp ON cmp.id = lr_entry.company_id