[jira] [Commented] (PHOENIX-476) Support declaration of DEFAULT in CREATE statement

["James Taylor (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PHOENIX-476?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15459018#comment-15459018 ] 

James Taylor commented on PHOENIX-476:
--------------------------------------

[~kliew] - would you be interested in this one? We could do it in two stages:
#. Allow only constants (i.e. ParseNode.isStateless() of true).
#. Allow things like CURRENT_DATE and NEXT VALUE FOR expressions which evaluate to constants, but must be evaluated per statement so they're a bit trickier.

> Support declaration of DEFAULT in CREATE statement
> --------------------------------------------------
>
>                 Key: PHOENIX-476
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-476
>             Project: Phoenix
>          Issue Type: Task
>    Affects Versions: 3.0-Release
>            Reporter: James Taylor
>              Labels: enhancement
>
> Support the declaration of a default value in the CREATE TABLE/VIEW statement like this:
>     CREATE TABLE Persons (
>         Pid int NOT NULL PRIMARY KEY,
>         LastName varchar(255) NOT NULL,
>         FirstName varchar(255),
>         Address varchar(255),
>         City varchar(255) DEFAULT 'Sandnes'
>     )
> To implement this, we'd need to:
> 1. add a new DEFAULT_VALUE key value column in SYSTEM.TABLE and pass through the value when the table is created (in MetaDataClient).
> 2. always set NULLABLE to ResultSetMetaData.columnNoNulls if a default value is present, since the column will never be null.
> 3. add a getDefaultValue() accessor in PColumn
> 4.  for a row key column, during UPSERT use the default value if no value was specified for that column. This could be done in the PTableImpl.newKey method.
> 5.  for a key value column with a default value, we can get away without incurring any storage cost. Although a little bit of extra effort than if we persisted the default value on an UPSERT for key value columns, this approach has the benefit of not incurring any storage cost for a default value.
>     * serialize any default value into KeyValueColumnExpression
>     * in the evaluate method of KeyValueColumnExpression, conditionally use the default value if the column value is not present. If doing partial evaluation, you should not yet return the default value, as we may not have encountered the the KeyValue for the column yet (since a filter evaluates each time it sees each KeyValue, and there may be more than one KeyValue referenced in the expression). Partial evaluation is determined by calling Tuple.isImmutable(), where false means it is NOT doing partial evaluation, while true means it is.
>     * modify EvaluateOnCompletionVisitor by adding a visitor method for RowKeyColumnExpression and KeyValueColumnExpression to set evaluateOnCompletion to true if they have a default value specified. This will cause filter evaluation to execute one final time after all KeyValues for a row have been seen, since it's at this time we know we should use the default value.



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