blocks|key|1613829|text|您可以使用关联子查询来查找表2中每个日期的表1中最近的日期：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1613830|SELECT
++++t2.Date,
++++t2.USD,
++++t2.USD+*+(SELECT+t1.ExchangeRate+FROM+Table1+t1
++++++++++++++WHERE+t1.Date+<=+t2.Date
++++++++++++++ORDER+BY+DATEDIFF(t2.Date,+t1.Date)+LIMIT+1)+AS+ConvertedAmount
FROM+Table2+t2;|code-block|syntax|javascript|1613831|​|1613832|📷|atomic|offset|length|1613833|1613834|1613835|Demo|1613836|1613837|注意，这是一种不受控制的方法，因为表2中日期的两边可能有两个最近的日期，其中一个可能是任意选择的。实际上，这里一个更好的长期方法是使用一个日历表，它每天都有外汇汇率。|1613838|entityMap|0|IMAGE|mutability|IMMUTABLE|imageUrl|https://developer.qcloudimg.com/http-save/yehe-900000/4447032e9ff8aa69ce1392030b0ff2cf.png|imageAlt|1|LINK|MUTABLE|url|http://sqlfiddle.com/#!9/1c37a1/1^0|0|0|0|0|1|0|0|0|0|0|4|1|0|0|0^^$0|@$1|2|3|4|5|6|7|18|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|19|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|1A|8|@]|9|@]|A|$]]|$1|I|3|J|5|K|7|1B|8|@]|9|@$L|1C|M|1D|1|1E]]|A|$]]|$1|N|3|H|5|6|7|1F|8|@]|9|@]|A|$]]|$1|O|3|H|5|6|7|1G|8|@]|9|@]|A|$]]|$1|P|3|Q|5|6|7|1H|8|@]|9|@$L|1I|M|1J|1|1K]]|A|$]]|$1|R|3|H|5|6|7|1L|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|1M|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|1N|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11|12|-4]]|13|$5|14|Y|15|A|$16|17]]]]

You could use a correlated subquery which finds the closest date in table 1 for each date in table 2:

<pre><code>SELECT
 t2.Date,
 t2.USD,
 t2.USD * (SELECT t1.ExchangeRate FROM Table1 t1
 WHERE t1.Date &lt;= t2.Date
 ORDER BY DATEDIFF(t2.Date, t1.Date) LIMIT 1) AS ConvertedAmount
FROM Table2 t2;
</code></pre>

<a href="https://i.stack.imgur.com/XOnB4.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/XOnB4.png" alt="enter image description here"></a>

<a href="http://sqlfiddle.com/#!9/1c37a1/1" rel="nofollow noreferrer"><h2>Demo</h2></a>

Note this is something of an uncontrolled approach, because there could be two nearest dates in table 1 on either side of a date in table 2, and one might be chosen arbitrarily. Really, a better long term approach here would be to use a calendar table which just has forex rates for every day.

Right now I have 2 tables:

*Table1 -*

Date&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Exchange Rate

00/00/0000&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 0.6

4/1/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 0.81

4/2/2018&nbsp; &nbsp; &nbsp; &nbsp;0.82

5/1/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 0.83

5/2/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 0.81

5/3/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 0.82

&nbsp;

*Table2 -*

Date&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; USD

2/2/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 50

3/5/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 60

4/1/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 50

4/3/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 100

4/15/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 200

5/1/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 60

5/2/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 80

5/3/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 90

&nbsp;

I want to have a Table 3 that reflects the Converted Amount *Table3 -*

Date&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; USD&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Converted Amount

2/2/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 50&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 50*0.6 = 30

3/5/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 60&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 60*0.6 = 36

4/1/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 50&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 50*0.81 = 40.5

4/3/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 100&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 100*0.82 = 82

4/15/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 200&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 200*0.82 = 164

5/1/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 60&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 60*0.83 = 49.8

5/2/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 80&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 80*0.81 = 64.8

5/3/2018&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 90&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 90*0.82 = 73.8

&nbsp;

How would I make this happen in SQL? The original data is very big.

The thing is that I would like Table3's 4/15/2018 and 4/3/2018 converted_amount to follow the 4/2/2018 exchange rate, as there are no 4/15/2018 or 4/3/2018 exchange rate in Table1. Essentially I would like to have the missing exchange rate to follow their closest previous date's exchange rate.

Also, for all the dates prior to 4/1/2018, the exchange rate should follow Table1's 00/00/0000 exchange rate.

Really appreciate your help! Thank you so much!

How to choose the previous closest value in sql

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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现在我有两张桌子：*表1 -*​数据​00/00/0000​4/1 2018年/2018年​4/2/2018​5/1/2018​5/2 2018年/2018年​5/3/2018​​*表2 -*数据._~_​2/2/2018​3/5/2018/2018​4/1/2018​4/3/2018/2018​4/15/2018​5/1/2018​5/2/2018​5/3/2018​​我想要一个表3，它反映了转

问如何在sql中选择前一个最近的值
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