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https://issues.apache.org/jira/browse/TAJO-1005?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jaehwa Jung updated TAJO-1005:
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Assignee: (was: Jaehwa Jung)
> Sort on expression values including aggregation function should be supported.
> -----------------------------------------------------------------------------
>
> Key: TAJO-1005
> URL: https://issues.apache.org/jira/browse/TAJO-1005
> Project: Tajo
> Issue Type: Improvement
> Components: Planner/Optimizer
> Reporter: Hyunsik Choi
>
> h3. Background
> In Tajo, expression evaluation are performed at only three operators, Scan,
> Join, and Projection. An expression is divided into multiple sub expressions,
> and then they are placed into proper operators.
> h3. Problem
> See the following example:
> {code}
> SELECT sum(x) / 100 as b from lineitem order by b
> {code}
> Tajo evaluates expressions at three operators: scan, join, and projection.
> Aggregation functions are evaluated at groupby operator, and expressions
> including aggregation functions are evaluated at projection operator.
> But, sort operator is placed between aggregation function and projection. So,
> sort operator does not have any opportunity to take the result of some
> expression including aggregation functions.
> h3. Solution
> So far, projection operator is only topmost operator of all operators. To
> solve the above problem, we need to improve the order of operators.
> Especially, projection operator can be interleaved between all operators.
> More specially, we allow projection operator to be inserted between group-by
> and sort operators. If so, the above problem will be solved.
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