Josh Rosen created SPARK-27561:
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Summary: Support "lateral column alias references" to allow column
aliases to be used within SELECT clauses
Key: SPARK-27561
URL: https://issues.apache.org/jira/browse/SPARK-27561
Project: Spark
Issue Type: New Feature
Components: SQL
Affects Versions: 2.4.0
Reporter: Josh Rosen
Amazon Redshift has a feature called "lateral column alias references:
[https://aws.amazon.com/about-aws/whats-new/2018/08/amazon-redshift-announces-support-for-lateral-column-alias-reference/].
Quoting from that blogpost:
{quote}The support for lateral column alias reference enables you to write
queries without repeating the same expressions in the SELECT list. For example,
you can define the alias 'probability' and use it within the same select
statement:
{code:java}
select clicks / impressions as probability, round(100 * probability, 1) as
percentage from raw_data;
{code}
{quote}
There's more information about this feature on
[https://docs.aws.amazon.com/redshift/latest/dg/r_SELECT_list.html:]
{quote}The benefit of the lateral alias reference is you don't need to repeat
the aliased expression when building more complex expressions in the same
target list. When Amazon Redshift parses this type of reference, it just
inlines the previously defined aliases. If there is a column with the same name
defined in the FROM clause as the previously aliased expression, the column in
the FROM clause takes priority. For example, in the above query if there is a
column named 'probability' in table raw_data, the 'probability' in the second
expression in the target list will refer to that column instead of the alias
name 'probability'.
{quote}
It would be nice if Spark supported this syntax. I don't think that this is
standard SQL, so it might be a good idea to research if other SQL databases
support similar syntax (and to see if they implement the same column resolution
strategy as Redshift).
One possibly-related existing ticket: SPARK-9338, which discusses the use of
SELECT aliases in GROUP BY expressions.
/cc [~hvanhovell]
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