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https://issues.apache.org/jira/browse/HIVE-16496?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15979834#comment-15979834
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Dudu Markovitz commented on HIVE-16496:
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[~cartershanklin], thanks for your eye opening comments.
1. I've added some more use-case
2. You are right about the positional part - it is not much useful to this
syntax enhancement (but I do have an idea for another syntax enhancement that
intends to ease ad-hoc work and can use the positional concept. I'll open a new
ticket for it)
P.s.
I would strongly recommend against the use NATURAL JOIN.
Columns can be renamed, dropped or added, which leads to a logically broken
code.
> Enhance asterisk expression (as in "select *") with EXCLUDE clause
> ------------------------------------------------------------------
>
> Key: HIVE-16496
> URL: https://issues.apache.org/jira/browse/HIVE-16496
> Project: Hive
> Issue Type: Wish
> Components: Parser
> Reporter: Dudu Markovitz
>
> support the following syntax:
> {code}
> select * exclude (a,b,e) from t
> {code}
> which for a table t with columns a,b,c,d,e would be equal to:
> {code}
> select c,d from t
> {code}
> Please note that the EXCLUDE clause relates directly to its preceding
> asterisk.
> Here are some useful use cases:
> h3. use-case 1: join
> {code}
> select t1.* exclude (x), t2.* from t1 join t2 on t1.x=t2.x;
> {code}
> This supplies a very clean way to select all columns without getting
> "Ambiguous column reference" and without the need to specify all the columns
> of at least one of the tables.
>
> Currently, without this enhancement, the query would look something like this:
> {code}
> select a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,y,z,t2.* from t1 join t2
> on t1.x=t2.x;
> {code}
> Considering a table may hold hundreds or even thousands of column, this can
> be come very ugly and error prone.
> Often this require some scripting work.
> h3. use-case 2: view
> Creating views with all the tables columns except for some technical columns
>
> {code}
> create myview as select * exclude (cre_ts,upd_ts) from t;
> {code}
> h3. use-case 3: row_number
> Remove computational columns that are not needed in the final row-set, e.g. -
> retrieve the last record for each customer
> {code}
> select * exclude (rn)
> from (select t.*
> ,row_number() over (partition by customer_id order by ts desc)
> as rn
> from t
> ) t
>
> where rn = 1
> {code}
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