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From "Santhosh Srinivasan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-385) Should support 'null' as a constant
Date Wed, 19 Nov 2008 01:33:44 GMT

    [ https://issues.apache.org/jira/browse/PIG-385?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12648872#action_12648872
] 

Santhosh Srinivasan commented on PIG-385:
-----------------------------------------

The NULL constant can be used in any context where other constants or expressions are used.
The difference between constants and NULL constants will be the type inference. The interred
type for NULL will be based on the context. For example, in the statement used in the bug
report (shown below for reference), the type of null will be the same as the type of $0. By
default, the type of null will be a bytearray.

{code}

B = foreach A generate $0 > 0 ? $0 : null;

{code}

Casting null
-----------------

If the user chooses to, he/she can cast the null to the appropriate type. For example:

{code}

B = foreach A generate $0 > 0 ? $0 : (int)null;

{code}

Use of null with complex types
-------------------------------------------

Since complex types are made of simple types, the same rules (as stated above) apply. Null
constant as map keys will be disallowed.

Examples follow:

{code}

B = foreach A generate $0 > 0 ? $0 : {(null)};
-- here we have a bag with a tuple with a bytearray null constant

C = foreach A generate [2#null];
-- a map constant with key 2 and value bytearray null

D = foreach A generate [null#10];
--- error maps cannot have null keys
{code}

Open questions
----------------------

1. When nulls are stored using PigStorage and then read back using PigStorage, a distinction
between the various types of null cannot be made.

Thoughts/suggestions/comments welcome.

> Should support 'null' as a constant
> -----------------------------------
>
>                 Key: PIG-385
>                 URL: https://issues.apache.org/jira/browse/PIG-385
>             Project: Pig
>          Issue Type: New Feature
>          Components: impl
>    Affects Versions: types_branch
>            Reporter: Alan Gates
>            Priority: Minor
>             Fix For: types_branch
>
>
> It would be nice to be able to do things like:
> B = foreach A generate $0 > 0 ? $0 : null;
> but right now null is not allowed as a constant.  This null constant should be allowed
anywhere an expression would be, and should be castable (that is (int)null).

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