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https://issues.apache.org/jira/browse/PHOENIX-1580?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14342633#comment-14342633
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Maryann Xue commented on PHOENIX-1580:
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[~aliciashu] By saying temporary PTable instance, I do NOT mean a temporary
HBase or Phoenix table. It's just a schema (not the schema as in schema name /
table name) for your data. The PTable instance will be used to construct a
ColumnResolver which decides how columns are compiled to Expressions. For
example, a ColumnResolver based on a PTable instance for a physical Phoenix
table will compile columns to either RowKeyColumnExpression or
KeyValueColumnExpression, which evaluate column values from HBase KVs. But in
some cases, we would process raw HBase KVs and project them into a different
representation, and compiler would know how to compile the columns into the
right type of Expressions to make sure that the new data representation is
interpreted and evaluated the right way.
Let's take a derived table case for example. Suppose we have a query like
"SELECT t.c, count(*) FROM (SELECT count(*) c FROM aTable GROUP BY a_string) AS
t GROUP BY t.c". The first step is to run the inner query, and the outer query
iterator would take the ResultIterator returned by the inner query and continue
to process, like you said, in a streaming fashion. But the outer query does not
have to know how data is retrieved or processed by the inner query, but it has
to know the schema of the result returned by the inner query, or say, how each
row of the inner query should be interpreted. That schema is created at
compiletime, on which the outer query compilation is based. The temporary
schema (PTable instance) here is definitely different from the physical table
"aTable", it's instead something like temporary table "t" with one column "c".
I believe taking a closer look at the code in QueryCompiler and the
FromCompiler would help a lot in understanding this logic.
> Support UNION ALL
> -----------------
>
> Key: PHOENIX-1580
> URL: https://issues.apache.org/jira/browse/PHOENIX-1580
> Project: Phoenix
> Issue Type: Bug
> Reporter: Alicia Ying Shu
> Assignee: Alicia Ying Shu
> Attachments: unionall-wipe.patch
>
>
> Select * from T1
> UNION ALL
> Select * from T2
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