Python 对 Pandas 数据集执行 SQL 查询
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Executing an SQL query over a pandas dataset
提问by Miguel Santos
I have a pandas data set, called 'df'.
我有一个名为“df”的熊猫数据集。
How can I do something like below;
我怎么能做下面的事情；
df.query("select * from df")
Thank you.
谢谢你。
For those who know R, there is a library called sqldf where you can execute SQL code in R, my question is basically, is there some library like sqldf in python
对于那些了解 R 的人来说，有一个叫做 sqldf 的库，你可以在 R 中执行 SQL 代码，我的问题基本上是，python 中有没有像 sqldf 这样的库
回答by YOBEN_S
This is not pandas.querysupposed to do , You can look at package pandasql(same like sqldfin R )
这不pandas.query应该做，您可以查看包pandasql（与sqldfR 中相同）
import pandas as pd
import pandasql as ps
df = pd.DataFrame([[1234, 'Customer A', '123 Street', np.nan],
[1234, 'Customer A', np.nan, '333 Street'],
[1233, 'Customer B', '444 Street', '333 Street'],
[1233, 'Customer B', '444 Street', '666 Street']], columns=
['ID', 'Customer', 'Billing Address', 'Shipping Address'])
q1 = """SELECT ID FROM df """
print(ps.sqldf(q1, locals()))
ID
0 1234
1 1234
2 1233
3 1233
回答by user1717828
You can use DataFrame.query(condition)to return a subset of the data frame matching conditionlike this:
您可以使用DataFrame.query(condition)返回匹配的数据框子集，condition如下所示：
df = pd.DataFrame(np.arange(9).reshape(3,3), columns=list('ABC'))
df
A B C
0 0 1 2
1 3 4 5
2 6 7 8
df.query('C < 6')
A B C
0 0 1 2
1 3 4 5
df.query('2*B <= C')
A B C
0 0 1 2
df.query('A % 2 == 0')
A B C
0 0 1 2
2 6 7 8
This is basically the same effect as an SQL statement, except the SELECT * FROM df WHEREis implied.
这与 SQL 语句的效果基本相同，只是SELECT * FROM df WHERE隐含了 。
回答by Zach Brookler
There's actually a new package that was just released, called dataframe_sql. This gives you the ability to query pandas dataframes using SQL just as you want to. You can find the package here https://github.com/zbrookle/dataframe_sql
实际上有一个刚刚发布的新包，称为dataframe_sql。这使您能够根据需要使用 SQL 查询 Pandas 数据帧。你可以在这里找到这个包https://github.com/zbrookle/dataframe_sql
