blocks|key|1439640|text|您可以使用默认的大小写：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1439641|UPDATE+table+SET+student+=+(CASE+WHEN+student+=+'10'+THEN+'100412'
+++++++++++++++++++++++++++++++++WHEN+student+=+'17'+THEN+'100295'+
+++++++++++++++++++++++++++++++++WHEN+student+=+'26'+THEN+'100981'
+++++++++++++++++++++++++++++++++ELSE+student
++++++++++++++++++++++++++++END)
WHERE+year+=+'2019';|code-block|syntax|javascript|1439642|否则，如果希望最小化负载，只需将所有已知的student值添加到WHERE子句中即可。这只会触发对真正受更改影响的行的更新。|offset|length|style|CODE|1439643|entityMap^0|0|0|L|7|W|5|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]|$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|N|$]]

You could use a default case for that:

<pre><code>UPDATE table SET student = (CASE WHEN student = '10' THEN '100412'
 WHEN student = '17' THEN '100295' 
 WHEN student = '26' THEN '100981'
 ELSE student
 END)
WHERE year = '2019';
</code></pre>

Otherwise, if you want to minimize the load, just add all known <code>student</code> values to the <code>WHERE</code> clause. This triggers an update only on those rows that are really affected by a change

blocks|key|1819306|text|我认为有两个解决办法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1819307|1819308|添加where子句|ordered-list-item|1819309|1819310|UPDATE+table+SET+student+=+(CASE+WHEN+student+=+'10'+THEN+'100412'
+++++++++++++++++++++++++++++++++WHEN+student+=+'17'+THEN+'100295'+
+++++++++++++++++++++++++++++++++WHEN+student+=+'26'+THEN+'100981'
++++++++++++++++++++++++++++END)
WHERE+year+=+'2019'+AND+student+IN+('10','17','26');|code-block|syntax|javascript|1819311|1819312|使用else语句，但这将扫描整个表，没有结果:|1819313|1819314|UPDATE+table+SET+student+=+(CASE+WHEN+student+=+'10'+THEN+'100412'
+++++++++++++++++++++++++++++++++WHEN+student+=+'17'+THEN+'100295'+
+++++++++++++++++++++++++++++++++WHEN+student+=+'26'+THEN+'100981'
+++++++++++++++++++++++++++++++++ELSE+student
++++++++++++++++++++++++++++END)
WHERE+year+=+'2019';|1819315|entityMap^0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|U|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|V|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|W|8|@]|9|@]|A|$]]|$1|G|3|H|5|I|7|X|8|@]|9|@]|A|$J|K]]|$1|L|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|M|3|N|5|E|7|Z|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|10|8|@]|9|@]|A|$]]|$1|P|3|Q|5|I|7|11|8|@]|9|@]|A|$J|K]]|$1|R|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|S|$]]

There a two solutions I think :

<ol>
<li>Add a where clause</li>
</ol>

<pre><code>UPDATE table SET student = (CASE WHEN student = '10' THEN '100412'
 WHEN student = '17' THEN '100295' 
 WHEN student = '26' THEN '100981'
 END)
WHERE year = '2019' AND student IN ('10','17','26');
</code></pre>

<ol start="2">
<li>Use else statement but that will scan the whole table for nothing :</li>
</ol>

<pre><code>UPDATE table SET student = (CASE WHEN student = '10' THEN '100412'
 WHEN student = '17' THEN '100295' 
 WHEN student = '26' THEN '100981'
 ELSE student
 END)
WHERE year = '2019';
</code></pre>

blocks|key|1439675|text|对于跳过记录，而不是在case语句中，您可以使用这样的方法|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1439676|UPDATE+table+SET+student+=+(CASE+WHEN+student+=+'10'+THEN+'100412'
+++++++++++++++++++++++++++++++++WHEN+student+=+'17'+THEN+'100295'+
+++++++++++++++++++++++++++++++++WHEN+student+=+'26'+THEN+'100981'
++++++++++++++++++++++++++++END)
WHERE+year+=+'2019'+AND+student+IN+('10','17','26');|code-block|syntax|javascript|1439677|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

For skipping records not in case statement, you can use something like this

<pre><code>UPDATE table SET student = (CASE WHEN student = '10' THEN '100412'
 WHEN student = '17' THEN '100295' 
 WHEN student = '26' THEN '100981'
 END)
WHERE year = '2019' AND student IN ('10','17','26');
</code></pre>

blocks|key|503166|text|您可以使用in或=运算符。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|503167|WHERE+year+=+'2019'+AND+(student+=+'10'+or+student+=+'17'+or+student++='26');|code-block|syntax|javascript|503168|entityMap^0|5|2|8|1|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

You can use <code>in</code> or <code>=</code> operator

<pre><code>WHERE year = '2019' AND (student = '10' or student = '17' or student ='26');
</code></pre>

How do you ignore records not inside the case statement when using CASE/WHEN/THEN?

For example, this statement will update three matching records as expected but will make all student records that do not match a WHEN/THEN clause to NULL

<pre><code>UPDATE table SET student = (CASE WHEN student = '10' THEN '100412'
 WHEN student = '17' THEN '100295' 
 WHEN student = '26' THEN '100981'
 END)
WHERE year = '2019';
</code></pre>

How can you skip over records not inside the CASE statement and only change records that have a matching clause?

MySQL UPDATE -- ignore records not in CASE statement

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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在使用case / the /然后时，如何忽略不在CASE语句中的记录？例如，该语句将按预期更新三条匹配记录，但使所有不匹配时间/然后子句的学生记录变为空UPDATE table SET student = (CASE WHEN student = '10' THEN '100412'                 ...

问MySQL更新--忽略不使用CASE语句的记录
EN

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问MySQL更新--忽略不使用CASE语句的记录EN