cx_Oracle:如何迭代结果集? [英] cx_Oracle: How do I iterate over a result set?

问题描述

有几种方法可以遍历结果集.两者的权衡是什么?

There are several ways to iterate over a result set. What are the tradeoff of each?

推荐答案

规范的方法是使用内置的游标迭代器.

The canonical way is to use the built-in cursor iterator.

curs.execute('select * from people')
for row in curs:
    print row

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您可以使用fetchall()一次获取所有行.

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You can use fetchall() to get all rows at once.

for row in curs.fetchall():
    print row

使用它来创建包含返回值的Python列表可能会很方便:

It can be convenient to use this to create a Python list containing the values returned:

curs.execute('select first_name from people')
names = [row[0] for row in curs.fetchall()]

这对于较小的结果集很有用，但是如果结果集很大，可能会有不良的副作用.

This can be useful for smaller result sets, but can have bad side effects if the result set is large.

• 您必须等待整个结果集返回到 您的客户流程.

• You have to wait for the entire result set to be returned to your client process.

您可能会吞噬客户端中的大量内存以进行保存 内置列表.

You may eat up a lot of memory in your client to hold the built-up list.

Python可能需要一段时间才能构造和解构 列出您将要立即丢弃的内容.

It may take a while for Python to construct and deconstruct the list which you are going to immediately discard anyways.

如果您知道结果集中将返回单行，则可以调用fetchone()来获取单行.

If you know there's a single row being returned in the result set you can call fetchone() to get the single row.

curs.execute('select max(x) from t')
maxValue = curs.fetchone()[0]

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最后，您可以循环遍历结果集，一次获取一行.通常，与使用迭代器相比，这样做没有什么特别的优势.

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Finally, you can loop over the result set fetching one row at a time. In general, there's no particular advantage in doing this over using the iterator.

row = curs.fetchone()
while row:
    print row
    row = curs.fetchone()

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