擅长:python、mysql、java
<h3><code>merge</code>与<code>pd.concat</code></h3>
<pre><code>m = df1.mobile_no.isna()
merged_df = pd.concat([df1.loc[m], df1.loc[~m].merge(df2, on='mobile_no', how ='left')]).sort_index()
</code></pre>
<h3>输出</h3>
<pre><code> name mobile_no download_date
0 Hector ABC 123 2021-05-30
1 Hector ABC 287 2020-09-28
2 Jose JKD 567 NaN
3 Luis AH <NA> NaN
3 Harry AC 569 2020-01-15
4 Billy DH <NA> NaN
</code></pre>