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https://issues.apache.org/jira/browse/PIG-4608?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14596469#comment-14596469
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Rohini Palaniswamy commented on PIG-4608:
-----------------------------------------
The problem with the implicit add is that user typos could make it an add
instead of update. For eg: If user specified
updated = FOREACH three_numbers UPDATE_STRICT 3 AS f3, 6 AS f7;
but actually meant to say 6 AS f6; , then the script will run fine and will
require more debugging to find why the output is not as expected. So would
prefer having ... at the end to make any additions explicit. That way one can
throw errors for update of columns that do not exist.
> FOREACH ... UPDATE
> ------------------
>
> Key: PIG-4608
> URL: https://issues.apache.org/jira/browse/PIG-4608
> Project: Pig
> Issue Type: New Feature
> Reporter: Haley Thrapp
>
> I would like to propose a new command in Pig, FOREACH...UPDATE.
> Syntactically, it would look much like FOREACH … GENERATE.
> Example:
> Input data:
> (1,2,3)
> (2,3,4)
> (3,4,5)
> -- Load the data
> three_numbers = LOAD 'input_data'
> USING PigStorage()
> AS (f1:int, f2:int, f3:int);
> -- Sum up the row
> updated = FOREACH three_numbers UPDATE
> 5 as f1,
> f1+f2 as new_sum
> ;
> Dump updated;
> (5,2,3,3)
> (5,3,4,5)
> (5,4,5,7)
> Fields to update must be specified by alias. Any fields in the UPDATE that do
> not match an existing field will be appended to the end of the tuple.
> This command is particularly desirable in scripts that deal with a large
> number of fields (in the 20-200 range). Often, we need to only make
> modifications to a few fields. The FOREACH ... UPDATE statement, allows the
> developer to focus on the actual logical changes instead of having to list
> all of the fields that are also being passed through.
> My team has prototyped this with changes to FOREACH ... GENERATE. We believe
> this can be done with changes to the parser and the creation of a new
> LOUpdate. No physical plan changes should be needed because we will leverage
> what LOGenerate does.
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