PavithraRamachandran opened a new pull request #25628: [SPARK-28897][Core]'coalesce' error when executing dataframe.na.fill URL: https://github.com/apache/spark/pull/25628 ### What changes were proposed in this pull request? **Root Cause:** When a dataframe is created using select statement (using **spark.sql.parser.quotedRegexColumnNames=true**) dataframe fill is called- the _fillCol_ in DataFrameNaFunctions, **``(backtick)** are added explicitly to the **columnNames**, the column name is misunderstood to be a regex and it is set as an unresolvedregex, which makes the coalesce resolving to fail. _Observation_ When we create the dataframe from the select statement using a regex, valid columns names are returned after applying the filter(regex). So adding _backticks_ to column name in this flow was not needed. To check the impact, select statement with regex were used, there was no impact while executing without the _backticks_. **After Fix** While passing the columnname to the dataframe column method, **``(backtick)** are not added, as the value that is received is not a regular expression, but a valid column name. ### Why are the changes needed? By doing this change column name is not considered as regex and the proper Column function is derived. And does not fail to resolve the expression. ### Does this PR introduce any user-facing change? No ### How was this patch tested? The patch was tested by adding UT cases. And testing in spark shell using various select statement .(with and without regex) Before Fix:  After Fix: 
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