Chunjun Xiao created SPARK-30618:
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             Summary: Why does SparkSQL allow `WHERE` to be table alias?
                 Key: SPARK-30618
                 URL: https://issues.apache.org/jira/browse/SPARK-30618
             Project: Spark
          Issue Type: Question
          Components: SQL
    Affects Versions: 2.4.4
            Reporter: Chunjun Xiao


An empty `WHERE` expression is valid in Spark SQL, as: `SELECT * FROM XXX 
WHERE`. Here `WHERE` is parsed as the table alias.

I think this surprises most SQL users, as this is an invalid statement in some 
SQL engines like MySQL.  

I checked the source code, and found more keywords (in most SQL system) are 
treated as `noReserved` and allowed to be table alias.  

Could anyone please give the rationality behind this decision?



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