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https://issues.apache.org/jira/browse/PHOENIX-939?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13982143#comment-13982143
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Prashant Kommireddi commented on PHOENIX-939:
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[[email protected]] - ah, so that can be reused.
[~jamestaylor]
{quote}
it's a positional mapping, right?
{quote}
That's correct.
{quote}Is the AS (a:chararray, b:chararray, c: long, d:int) optional?{quote}
Yes. You can use positional notation ($0, $1, $2, $3) in which case.
{quote}Does Pig restrict the names of the elements in a relation? {quote}
Yes. See http://pig.apache.org/docs/r0.12.1/basic.html#identifiers
{quote}The relation would be "ID", "UPPER(NAME)","NEXT VALUE FOR
my_seq","MY_NUM+1". Would this confuse Pig?{quote}
Expressions might not always be valid identifiers. It's safer IMO to have the
user provide the identifiers.
{quote}Can you also refer to the elements of a relation by position like you
can in JDBC: resultSet.getInt(4)?{quote}
Yes. Positional notation is generated by the system. Positional notation is
indicated with the dollar sign ($) and begins with zero (0); for example, $0,
$1, $2.
> Generalize SELECT expressions for Pig Loader
> --------------------------------------------
>
> Key: PHOENIX-939
> URL: https://issues.apache.org/jira/browse/PHOENIX-939
> Project: Phoenix
> Issue Type: Improvement
> Affects Versions: 5.0.0, 3.1, 4.1
> Reporter: James Taylor
> Assignee: maghamravikiran
> Fix For: 5.0.0, 3.1, 4.1
>
>
> The current Pig Loader requires that the query contain only column references
> in the SELECT expressions. Instead, we should allow any expression as that
> will provide more general utility. For example, built-in functions, sequence
> references, etc. could be used then.
> Validation can be done by simply compiling the query. This does all the
> validation required. It's ok if it's compiled twice if need be too.
> Pig doesn't know and likely wouldn't care if the expressions in the SELECT
> correspond to columns in Phoenix or general expressions. You can use the
> ColumnProjection.getName() method to get back an alias of the SELECT
> expression. If no alias is provided, then the String of the expression is
> returned. [~prkommireddi] - can you weigh in here? You can use the Phoenix
> RowProjector to iterate through each ColumnProjector you get back after the
> compile to get the alias of the select expression (i.e. you'd give this to
> Pig as the "column" name) plus the data type. Note that if this is
> problemattic, then you could likely generate an alias name if one is not
> present.
> For example:
> {code}
> RowProjector rowProj = queryPlan.getProjector();
> for (ColumnProjector colProj : rowProj.getColumnProjectors()) {
> String columnName = colProj.getName();
> PDataType dataType = colProj.getExpression().getDataType();
> }
> {code}
> If the SELECT expressions are simple column references, this would be exactly
> the same as is being done now. If the SELECT expressions are more complex
> expressions, this would work as well.
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