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Reproducible Example

import pandas as pd

a = pd.DataFrame({0:[1,2,3]})
b = pd.DataFrame(index=[1,2,3],data={0:[4,5,6]})
a.join(b, on=0, rsuffix='_test')

Issue Description

When dataframe a and b have the same column name, a key_ column is created unexpectedly after the join operation.

key_0 0 0_test
0 1 1 4
1 2 2 5
2 3 3 6

Expected Behavior

Expecting result without the key_0 column.

Installed Versions