blocks|key|2308626|text|这是因为该示例使用元组(+...，)传递值|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2308627|值adr+=(“黄色花园2"，)是包含单个值元组|2308628|如果你只需要字符串，你可以试试|2308629|sql+=+"SELECT+*+FROM+customers+WHERE+address+LIKE+concat('%25',+%25s,+'%25')"

adr+=+"Yellow+Garden+2"
mycursor.execute(sql,+adr)++|code-block|syntax|javascript|2308630|或|2308631|mycursor.execute(sql,+"Yellow+Garden+2")+|2308632|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|S|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|T|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|H|7|V|8|@]|9|@]|A|$I|J]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

This happend because the example use a tuple ( ...,) for passing a value 
the value adr = ("Yellow Garden 2", ) is a tuple that contain a single value 

if you need just string you coudl try 

<pre><code>sql = "SELECT * FROM customers WHERE address LIKE concat('%', %s, '%')"

adr = "Yellow Garden 2"
mycursor.execute(sql, adr) 
</code></pre>

or 

<pre><code>mycursor.execute(sql, "Yellow Garden 2") 
</code></pre>

blocks|key|2308645|text|adr+=+("Yellow+Garden+2",+)|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|2308646|这将adr定义为只有一个元素的tuple。您可以使用以下命令进行验证：|unstyled|offset|length|style|CODE|2308647|type(adr)|2308648|应该是：|2308649|<class+'tuple'>|2308650|当您删除逗号,+(是逗号引起的，而不是空格)时，adr将变成一个简单的字符串：|2308651|adr+=+("Yellow+garden+2")
type(adr)|2308652|2308653|<type+'str'>|2308654|MySQL应用程序接口要求将tuple作为参数传递，因此出现错误。(soemthing,)就是您在python中定义单元素元组的方式。|2308655|entityMap^0|0|2|3|F|5|0|0|0|0|6|1|O|3|0|0|0|0|E|5|X|C|0^^$0|@$1|2|3|4|5|6|7|11|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|12|8|@$G|13|H|14|I|J]|$G|15|H|16|I|J]]|9|@]|A|$]]|$1|K|3|L|5|6|7|17|8|@]|9|@]|A|$B|C]]|$1|M|3|N|5|F|7|18|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|19|8|@]|9|@]|A|$B|C]]|$1|Q|3|R|5|F|7|1A|8|@$G|1B|H|1C|I|J]|$G|1D|H|1E|I|J]]|9|@]|A|$]]|$1|S|3|T|5|6|7|1F|8|@]|9|@]|A|$B|C]]|$1|U|3|N|5|F|7|1G|8|@]|9|@]|A|$]]|$1|V|3|W|5|6|7|1H|8|@]|9|@]|A|$B|C]]|$1|X|3|Y|5|F|7|1I|8|@$G|1J|H|1K|I|J]|$G|1L|H|1M|I|J]]|9|@]|A|$]]|$1|Z|3|-4|5|F|7|1N|8|@]|9|@]|A|$]]]|10|$]]

<pre><code>adr = ("Yellow Garden 2", )
</code></pre>

This defines <code>adr</code> to be a <code>tuple</code> with a single element. You can verify with:

<pre><code>type(adr)
</code></pre>

Should be:

<pre><code>&lt;class 'tuple'&gt;
</code></pre>

When you remove the comma <code>,</code> (it's the comma that's causing it, not the blank space), <code>adr</code> becomes a simple string:

<pre><code>adr = ("Yellow garden 2")
type(adr)
</code></pre>

Should be:

<pre><code>&lt;type 'str'&gt;
</code></pre>

The MySQL API expects a <code>tuple</code> to be passed as arguments, hence the error. And the <code>(soemthing,)</code> is just how you define single-element tuples in python.

blocks|key|2520429|text|这个答案是基于this+blog+post的。execute的第二个参数是一个元组，需要一个悬空逗号，但前提是元组中只有一个元素。正如博客所讨论的，悬空逗号需要区分：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2520430|("Yellow+Garden+2",)|code-block|syntax|javascript|2520431|元组，来自：|2520432|("Yellow+Garden+2")|2520433|文字字符串表达式。或者，至少(1)对于您想让它成为元组还是算术表达式是不明确的。|2520434|但是，在有两个或更多参数的情况下，悬空逗号应该是可选的，例如|2520435|sql+=+"SELECT+*+FROM+customers+WHERE+address+LIKE+%25s+OR+address+LIKE+%25s"
adr+=+("Yellow+Garden+1",+"Yellow+Garden+2")
mycursor.execute(sql,+adr)|2520436|编辑：|BOLD|2520437|我还要补充的是，在这里使用元组中的悬空逗号可能是最佳的编程实践。为什么？假设您编写了一些代码，这些代码最初使用了一个包含两个元素的元组。从技术上讲，您不需要悬空逗号。但是，在未来，有人可能会重构并删除一个元素。如果您没有包含悬空逗号，那么代码可能会崩溃。|2520438|entityMap|0|LINK|mutability|MUTABLE|url|https://ubuntuforums.org/archive/index.php/t-2232993.html^0|N|7|7|E|0|0|0|0|0|E|3|0|0|0|0|3|0|0^^$0|@$1|2|3|4|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@$9|1A|A|1B|1|1C]]|E|$]]|$1|F|3|G|5|H|7|1D|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1E|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|1F|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1G|8|@$9|1H|A|1I|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|6|7|1J|8|@]|D|@]|E|$]]|$1|S|3|T|5|H|7|1K|8|@]|D|@]|E|$I|J]]|$1|U|3|V|5|6|7|1L|8|@$9|1M|A|1N|B|W]]|D|@]|E|$]]|$1|X|3|Y|5|6|7|1O|8|@]|D|@]|E|$]]|$1|Z|3|-4|5|6|7|1P|8|@]|D|@]|E|$]]]|10|$11|$5|12|13|14|E|$15|16]]]]

I based this answer off <a href="https://ubuntuforums.org/archive/index.php/t-2232993.html" rel="nofollow noreferrer">this blog post</a>. The second parameter to <code>execute</code> is a tuple, and a dangling comma is required, but only if the tuple has just one element in it. As the blog discusses, the dangling comma is required to distinguish:

<pre><code>("Yellow Garden 2",)
</code></pre>

the tuple, from:

<pre><code>("Yellow Garden 2")
</code></pre>

the literal string expression. Or, at least <code>(1)</code> would be ambiguous as to whether you intended for it to be a tuple or arithmetic expression.

However, in the case of two or more parameters, the dangling comma should be optional, e.g.

<pre><code>sql = "SELECT * FROM customers WHERE address LIKE %s OR address LIKE %s"
adr = ("Yellow Garden 1", "Yellow Garden 2")
mycursor.execute(sql, adr)
</code></pre>

Edit:

I will add also that it might be considered best programming practice to always use the dangling comma in a tuple here. Why? Let's say you authored some code which initially used a tuple with two elements in it. You would technically not need the dangling comma. But then, in the future, someone might refactor and remove one element. If you had not included the dangling comma, then the code might break.

I'm following a Python tutorial at <a href="https://www.w3schools.com/python/python_mysql_where.asp" rel="nofollow noreferrer">W3school</a>.

<pre class="lang-py prettyprint-override"><code>mycursor = mydb.cursor()

sql = "SELECT * FROM customers WHERE address LIKE %s"
adr = ("Yellow Garden 2", ) // I don't understand this part!!!

mycursor.execute(sql, adr) 

myresult = mycursor.fetchall()

for x in myresult:
 print(x)
</code></pre>

If I run the above code, I get the following result. 
<a href="https://i.stack.imgur.com/ncLXx.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ncLXx.png" alt="enter image description here"></a>

However when I remove a blank space after a comma, I get an error. 
<code>adr = ("Yellow Garden 2", )</code> --> <code>adr = ("Yellow Garden 2" )</code>

1) I want to know why I need a blank space after a comma.

2) Why do I need a bracket ( ) ,too? (When I remove the brackets, I also get an error.) Like <code>adr = "Yellow Garden 2"</code>

Where clause with a dangling comma in Python

Python

MySQL

我在上学习Python教程。mycursor = mydb.cursor()sql = "SELECT * FROM customers WHERE address LIKE %s"adr = ("Yellow Garden 2", )        // I don't understand this part!!!...

问Python中带有悬空逗号的Where子句
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