[jira] [Resolved] (IMPALA-9661) Avoid introducing unused columns in table masking view

["Quanlong Huang (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/IMPALA-9661?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Quanlong Huang resolved IMPALA-9661.
------------------------------------
    Fix Version/s: Impala 4.0
       Resolution: Fixed

> Avoid introducing unused columns in table masking view
> ------------------------------------------------------
>
>                 Key: IMPALA-9661
>                 URL: https://issues.apache.org/jira/browse/IMPALA-9661
>             Project: IMPALA
>          Issue Type: Bug
>          Components: Frontend
>            Reporter: Quanlong Huang
>            Assignee: Quanlong Huang
>            Priority: Critical
>             Fix For: Impala 4.0
>
>
> If a table has column masking policies, we replace its unanalyzed TableRef with an analyzed InlineViewRef (table masking view) in FromClause.analyze(). However, we can't detect which columns are actually used in the original query at this point. In fact, analyze() for SelectList, WhereClause, GroupByClause and other clauses containing SlotRefs happen after FromClause.analyze(). After the whole query block is analyzed, we can get the exact set of required columns. We should do table masking there to avoid introducing unused columns.
> To be specifit, if table _tbl_(_id_ int, _name_ string, _address_ string) has column masking policies for column _name_ and _address_ to mask them, the following query
> {code:sql}
> select name from tbl where id > 10;
> {code}
> will be rewritten to
> {code:sql}
> select name from (
>   select id, mask(name) as name, mask(address) as address from tbl
> ) tbl where id > 10;
> {code}
> The rewritten query introduce the requirement for SELECT privilege on the _address_ column which isn't required by the original query. We should either fix this or IMPALA-9223.



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