blocks|key|1553007|text|rowcount是指受最后一次操作影响的行数。因此，如果您执行insert并只插入一行，则它将返回1。如果您更新200行，则它将返回200。另一方面，如果使用SELECT，最后一个操作实际上并不影响行，它是一个结果集。在这种情况下，0在语法上是不正确的，因此接口返回-1。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1553008|它还将为您执行设置变量或使用create/alter命令等操作的操作返回-1。|1553009|entityMap^0|0|8|V|6|27|6|38|1|3P|2|0|10|2|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]|$9|Q|A|R|B|C]|$9|S|A|T|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|X|8|@]|D|@]|E|$]]]|I|$]]

<code>rowcount</code> refers to the number of rows affected by the last operation. So, if you do an <code>insert</code> and insert only one row, then it will return 1. If you update 200 rows, then it will return 200. On the other hand, if you <code>SELECT</code>, the last operation doesn't really affect rows, it is a result set. In that case, <code>0</code> would be syntactically incorrect, so the interface returns <code>-1</code> instead.

It will also return <code>-1</code> for operations where you do things like set variables or use create/alter commands.

blocks|key|1553041|text|您正在连接的数据库无法为您的查询提供该数字。许多数据库引擎在您获取结果时生成行，并在您执行此操作时扫描其内部表和索引数据结构以查找下一个匹配结果。在获取所有行之前，引擎无法知道最终的计数。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1553042|当行数未知时，Python+DB-API+2.0+specification+for+Cursor.rowcount声明在这种情况下必须将行数设置为-1：|offset|length|style|CODE|1553043|1553044|属性为-1，以防...接口无法确定最后一个操作的行数。|blockquote|1553045|1553046|1553047|pyodbc+Cursor.rowcount+documentation符合以下要求：|1553048|1553049|最后一条SQL语句修改的行数。|1553050|1553051|如果没有执行SQL或行数未知，则为-1。注意，出于性能原因，数据库在SQL+select语句后立即报告的情况并不少见。(在将第一条记录返回给应用程序之前，可能不知道确切的数字。)|1553052|1553053|Cursor.rowcount+documentation并不是唯一的例子，另一个易于链接的例子是Python标准库pyodbc模块；它的pyodbc声明：|1553054|根据Python+DB+API规范的要求，|1553055|属性“如果没有在游标上执行executeXX()或者接口不能确定最后一个操作的行数，则为-1”。这包括SELECT语句，因为在提取所有行之前，我们无法确定查询生成的行数。|1553056|1553057|1553058|请注意，对于数据库实现的子集，可以在获取某些行之后更新行计数值。您必须检查您要连接到的特定数据库文档，看看这些实现是否可以做到这一点，或者行数是否必须保持为-1。当然，你可以随时进行实验。|1553059|您可以首先执行COUNT()+select，或者，如果预期结果集不会太大，则使用cursor.fetchall()并对结果列表使用len()。|1553060|entityMap|0|LINK|mutability|MUTABLE|url|https://www.python.org/dev/peps/pep-0249/#rowcount|1|https://github.com/mkleehammer/pyodbc/wiki/Cursor|2|https://docs.python.org/3/library/sqlite3.html#sqlite3.Cursor.rowcount^0|0|17|F|22|2|7|1F|0|0|0|3|2|0|0|0|7|F|7|T|1|0|0|0|0|0|0|0|F|0|T|2|0|0|D|B|1F|6|0|0|0|0|7|7|14|H|1T|5|0^^$0|@$1|2|3|4|5|6|7|1K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1L|8|@$D|1M|E|1N|F|G]|$D|1O|E|1P|F|G]]|9|@$D|1Q|E|1R|1|1S]]|A|$]]|$1|H|3|-4|5|6|7|1T|8|@]|9|@]|A|$]]|$1|I|3|J|5|K|7|1U|8|@$D|1V|E|1W|F|G]]|9|@]|A|$]]|$1|L|3|-4|5|6|7|1X|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|1Y|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|1Z|8|@$D|20|E|21|F|G]]|9|@$D|22|E|23|1|24]]|A|$]]|$1|P|3|-4|5|6|7|25|8|@]|9|@]|A|$]]|$1|Q|3|R|5|K|7|26|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|27|8|@]|9|@]|A|$]]|$1|T|3|U|5|6|7|28|8|@]|9|@]|A|$]]|$1|V|3|-4|5|6|7|29|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|2A|8|@$D|2B|E|2C|F|G]]|9|@$D|2D|E|2E|1|2F]]|A|$]]|$1|Y|3|Z|5|6|7|2G|8|@]|9|@]|A|$]]|$1|10|3|11|5|K|7|2H|8|@$D|2I|E|2J|F|G]|$D|2K|E|2L|F|G]]|9|@]|A|$]]|$1|12|3|-4|5|6|7|2M|8|@]|9|@]|A|$]]|$1|13|3|-4|5|6|7|2N|8|@]|9|@]|A|$]]|$1|14|3|15|5|6|7|2O|8|@]|9|@]|A|$]]|$1|16|3|17|5|6|7|2P|8|@$D|2Q|E|2R|F|G]|$D|2S|E|2T|F|G]|$D|2U|E|2V|F|G]]|9|@]|A|$]]|$1|18|3|-4|5|6|7|2W|8|@]|9|@]|A|$]]]|19|$1A|$5|1B|1C|1D|A|$1E|1F]]|1G|$5|1B|1C|1D|A|$1E|1H]]|1I|$5|1B|1C|1D|A|$1E|1J]]]]

You are connecting to a database that can't give you that number for your query. Many database engines produce rows as you fetch results, scanning their internal table and index data structures for the next matching result as you do so. The engine can't know the final count until you fetched all rows.

When the rowcount is not known, the <a href="https://www.python.org/dev/peps/pep-0249/#rowcount" rel="noreferrer">Python DB-API 2.0 specification for <code>Cursor.rowcount</code></a> states the number must be set to <code>-1</code> in that case:

<blockquote>
 The attribute is <code>-1</code> in case [...] the rowcount of the last operation is cannot be determined by the interface.
</blockquote>

The pyodbc <a href="https://github.com/mkleehammer/pyodbc/wiki/Cursor" rel="noreferrer"><code>Cursor.rowcount</code> documentation</a> conforms to this requirement:

<blockquote>
 The number of rows modified by the last SQL statement.
 
 This is -1 if no SQL has been executed or if the number of rows is unknown. Note that it is not uncommon for databases to report -1 immediately after a SQL select statement for performance reasons. (The exact number may not be known before the first records are returned to the application.)
</blockquote>

pyodbc is not alone in this, another easy-to-link-to example is the Python standard library <code>sqlite3</code> module; it's <a href="https://docs.python.org/3/library/sqlite3.html#sqlite3.Cursor.rowcount" rel="noreferrer"><code>Cursor.rowcount</code> documentation</a> states:

<blockquote>
 As required by the Python DB API Spec, the rowcount attribute “is -1 in case no <code>executeXX()</code> has been performed on the cursor or the rowcount of the last operation is not determinable by the interface”. This includes <code>SELECT</code> statements because we cannot determine the number of rows a query produced until all rows were fetched.
</blockquote>

Note that for subset of database implementations, the rowcount value can be updated after fetching some of the rows. You'll have to check your specific database documentation you are connecting to to see if that implementations can do this, or if the rowcount must remain at -1. You could always experiment, of course.

You could execute a <code>COUNT()</code> select first, or, if the result set is not expected to be too large, use <code>cursor.fetchall()</code> and use <code>len()</code> on the resulting list.

blocks|key|3811705|text|如果您使用的是microsoft+sql+server，并且希望获得前一条select语句中返回的行数，则只需执行select+@@rowcount即可。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3811706|例如：|3811707|cursor.execute("select+@@rowcount")
rowcount+=+cursor.fetchall()[0][0]|code-block|syntax|javascript|3811708|entityMap^0|1L|H|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|R|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|S|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

If you are using microsoft sql server, and you want to get the number of rows returned in the prior select statement, you can just execute <code>select @@rowcount</code>.

E.g.:

<pre class="lang-py prettyprint-override"><code>cursor.execute("select @@rowcount")
rowcount = cursor.fetchall()[0][0]
</code></pre>

How does rowcount work. I am using pyodbc and it's always returning -1.

<pre><code> return_query = conn.query_db_param(query, q_params)
 print(return_query.rowcount)

 def query_db_param(self, query, params):
 self.cursor.execute(query,params)
 print(self.cursor.rowcount)
</code></pre>

pyodbc rowcount only returns -1

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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行数是如何工作的。我使用pyodbc，它总是返回-1。 return_query = conn.query_db_param(query, q_params) print(return_query.rowcount) def query_db_param(self, query, params):     self.c...

问pyodbc rowcount仅返回-1
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问pyodbc rowcount仅返回-1EN