点击图片查看表结构和问题 http://i.stack.imgur.com/odWKL.png
SELECT B.ENTITYID,
B.BALANCEDATE,
B.BALANCE,
MIN(DATEDIFF(DAY,B.BALANCEDATE,C.STATUSDATE)) RECENT
FROM BALANCES B JOIN STATUS C ON B.ENTITYID = C.ENTITYID
GROUP BY B.ENTITYID, B.BALANCEDATE,B.BALANCE
HAVING B.ENTITYID =1
我已经尝试了以下方法，但由于更多的嵌套选择在访问类似属性时存在问题，因此无法走得更远：
如果您正在使用 SQL Server，请参阅@ljh 的答案。下面的解决方案适用于 MySQL。由于 MySQL 不支持CTE和Window Function.
SET @entity_name = 'ABCD';
SELECT b.*, d.Status
FROM Entity a
INNER JOIN Balances b
ON a.EntityID = b.EntityID
LEFT JOIN
(
SELECT a.EntityID,
a.StatusDate StartDate,
b.StatusDate + Interval -1 DAY EndDate,
a.Status
FROM
(
SELECT b.*, @r1 := @r1 + 1 AS Row_number
FROM `Entity` a
INNER JOIN Status b
ON a.EntityID = b.EntityID
CROSS JOIN (SELECT @r1 := 0) rowCount
WHERE a.EntityName = @entity_name
ORDER BY b.Status ASC
) a
LEFT JOIN
(
SELECT b.*, @r2 := @r2 + 1 AS Row_number
FROM `Entity` a
INNER JOIN Status b
ON a.EntityID = b.EntityID
CROSS JOIN (SELECT @r2 := 1) rowCount
WHERE a.EntityName = @entity_name
ORDER BY b.Status ASC
) b ON a.Row_number = b.Row_number
) d
ON b.BalanceDate BETWEEN d.StartDate AND d.EndDate
WHERE a.EntityName = @entity_name
由于 MySQL 不支持Windowing Function等ROW_NUMBER()，因此下面的查询用于为每条记录User Variable提供类似的行号ROW_NUMBER()，然后将用于连接另一个子查询。
SELECT b.*, @r1 := @r1 + 1 AS Row_number
FROM `Entity` a
INNER JOIN Status b
ON a.EntityID = b.EntityID
CROSS JOIN (SELECT @r1 := 0) rowCount
WHERE a.EntityName = @entity_name
ORDER BY b.Status ASC
输出
╔══════════╦═════════════════════════════════╦════════╦════════════╗
║ ENTITYID ║ STATUSDATE ║ STATUS ║ ROW_NUMBER ║
╠══════════╬═════════════════════════════════╬════════╬════════════╣
║ 1 ║ May, 29 2010 00:00:00+0000 ║ A ║ 1 ║
║ 1 ║ April, 16 2010 00:00:00+0000 ║ B ║ 2 ║
║ 1 ║ April, 02 2010 00:00:00+0000 ║ C ║ 3 ║
║ 1 ║ February, 26 2010 00:00:00+0000 ║ D ║ 4 ║
╚══════════╩═════════════════════════════════╩════════╩════════════╝
为记录提供行号的主要目的是将其用于连接另一个子查询，以便我们可以得到StartDateand EndDatefor each Status。这很容易，SQL Server 2012因为它有一个名为LAG()的窗口函数
╔══════════╦═════════════════════════════════╦══════════════════════════════╦════════╗
║ ENTITYID ║ STARTDATE ║ ENDDATE ║ STATUS ║
╠══════════╬═════════════════════════════════╬══════════════════════════════╬════════╣
║ 1 ║ May, 29 2010 00:00:00+0000 ║ (null) ║ A ║
║ 1 ║ April, 16 2010 00:00:00+0000 ║ May, 28 2010 00:00:00+0000 ║ B ║
║ 1 ║ April, 02 2010 00:00:00+0000 ║ April, 15 2010 00:00:00+0000 ║ C ║
║ 1 ║ February, 26 2010 00:00:00+0000 ║ April, 01 2010 00:00:00+0000 ║ D ║
╚══════════╩═════════════════════════════════╩══════════════════════════════╩════════╝
一旦组织好状态范围。它现在是每个Balances.
最终结果
╔══════════╦═════════════════════════════════╦═════════╦════════╗
║ ENTITYID ║ BALANCEDATE ║ BALANCE ║ STATUS ║
╠══════════╬═════════════════════════════════╬═════════╬════════╣
║ 1 ║ May, 01 2010 00:00:00+0000 ║ 100 ║ B ║
║ 1 ║ April, 01 2010 00:00:00+0000 ║ 50 ║ D ║
║ 1 ║ March, 01 2010 00:00:00+0000 ║ 75 ║ D ║
║ 1 ║ February, 01 2010 00:00:00+0000 ║ 85 ║ (null) ║
╚══════════╩═════════════════════════════════╩═════════╩════════╝
上面演示的查询MySQL可以TSQL通过使用Common Table Expression和Window Function使用LAG() 轻松转换（仅在 SQL Server 2012 中引入）
WITH lookupTable
AS
(
SELECT EntityID,
StatusDate StartDate,
DATEADD(DAY, -1, LAG(StatusDate) OVER(PARTITION BY EntityID ORDER BY Status)) EndDate,
Status
FROM Status
)
SELECT b.*, d.Status
FROM Entity a
INNER JOIN Balances b
ON a.EntityID = b.EntityID
LEFT JOIN lookupTable d
ON b.BalanceDate BETWEEN d.StartDate AND d.EndDate AND
d.EntityID = a.EntityID
WHERE a.EntityName = 'ABCD'
输出
╔══════════╦═════════════════════════════════╦═════════╦════════╗
║ ENTITYID ║ BALANCEDATE ║ BALANCE ║ STATUS ║
╠══════════╬═════════════════════════════════╬═════════╬════════╣
║ 1 ║ May, 01 2010 00:00:00+0000 ║ 100 ║ B ║
║ 1 ║ April, 01 2010 00:00:00+0000 ║ 50 ║ D ║
║ 1 ║ March, 01 2010 00:00:00+0000 ║ 75 ║ D ║
║ 1 ║ February, 01 2010 00:00:00+0000 ║ 85 ║ (null) ║
╚══════════╩═════════════════════════════════╩═════════╩════════╝
以 SQL Server 2012 作为 RDBMS 为例。这是您需要的第一个查询。
这个答案使用了 SQL CTE（通用表表达式），它可能不适用于其他 RDBMS 系统。
SQL FIDDLE DEMO
查询说明：
1. 先连接[Balances] 和[Status] 表，使用BalanceDate > StatusDate 过滤结果，返回两个表的所有列，这是因为后面需要。
2.将步骤.1的输出与[Entity]表连接，使用EntityName过滤结果，仍然保留3个表中的所有列，当然不需要重复的EntityID。
3. 使用 CTE 保存连接
4. 使用 CTE 保存应用在连接输出上的排名
5. 使用 Rank number 过滤掉结果和按 BalanceDate 排序
;with CTE_AfterJoin
as
(
select E.EntityID, E.EnityName, C.BalanceDate, C.Balance, C.StatusDate, C.status
from Entity E
left join (
select B.EntityID, B.BalanceDate, B.Balance,S.StatusDate, S.[Status]
from Balances B
left join [Status] S
on B.EntityID = S.EntityID and B.BalanceDate > S.StatusDate
) C
on E.EntityID = C.EntityID
where E.EnityName = 'ABCD'
),
CTE_afterRank
as
(
select EnityName, BalanceDate, Balance,
rank() over (partition by BalanceDate order by StatusDate desc) as Rn, Status
from CTE_AfterJoin
)
select EnityName, BalanceDate, Balance, Status
from CTE_afterRank
where Rn = 1
order by BalanceDate desc
同样在 SQLServer2005+ 中，您可以将选项与APPLY()运算符一起使用。
APPLY 运算符允许您连接两个表表达式。每次对左表表达式中的每一行处理右表表达式。最终结果集包含从左表表达式中选择的所有列，然后是右表表达式的所有列。OUTER APLLY 对于右表表达式中没有对应匹配的那些行，它在右表表达式的列中包含 NULL 值。
SELECT e.EntityName, b.BalanceDate AS Date, b.Balance, o.Status
FROM Entity e JOIN Balances b ON e.EntityID = b.EntityID
OUTER APPLY (
SELECT TOP 1 s.Status AS Status
FROM Status s
WHERE b.EntityID = s.EntityID
AND s.StatusDate < b.BalanceDate
ORDER BY s.StatusDate DESC
) o
WHERE e.EntityName = 'ABCD'
为了提高性能（强制 INDEX SEEK 操作）将此索引与 INCLUDE 子句一起使用。INCLUDE 子句在最低/叶级别添加数据，而不是在索引树中。这使得索引更小，因为它不是树的一部分
CREATE INDEX x ON Status(StatusDate) INCLUDE(EntityID, Status)
CREATE INDEX x ON Entity(EntityName) INCLUDE(EntityID)
CREATE INDEX x ON Balances(EntityID, BalanceDate, Balance)
SQLFiddle上的演示
