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From "Matt McCline (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HIVE-20524) Schema Evolution checking is broken in going from Hive version 2 to version 3 for ALTER TABLE VARCHAR to DECIMAL
Date Sun, 09 Sep 2018 20:42:00 GMT

     [ https://issues.apache.org/jira/browse/HIVE-20524?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Matt McCline updated HIVE-20524:
--------------------------------
    Summary: Schema Evolution checking is broken in going from Hive version 2 to version 3
for ALTER TABLE VARCHAR to DECIMAL  (was: Schema Evolution checking is broken in going from
Hive ver 2 to ver 3 for ALTER TABLE VARCHAR to DECIMAL)

> Schema Evolution checking is broken in going from Hive version 2 to version 3 for ALTER
TABLE VARCHAR to DECIMAL
> ----------------------------------------------------------------------------------------------------------------
>
>                 Key: HIVE-20524
>                 URL: https://issues.apache.org/jira/browse/HIVE-20524
>             Project: Hive
>          Issue Type: Bug
>          Components: Hive
>            Reporter: Matt McCline
>            Assignee: Matt McCline
>            Priority: Critical
>         Attachments: HIVE-20524.01.patch
>
>
> Issue that started this JIRA:
> {code}
> create external table varchar_decimal (c1 varchar(25));
> alter table varchar_decimal change c1 c1 decimal(31,0);
> ERROR : FAILED: Execution Error, return code 1 from org.apache.hadoop.hive.ql.exec.DDLTask.
Unable to alter table. The following columns have types incompatible with the existing columns
in their respective positions :
> c1
> {code}
> There appear to be 2 issues here:
> 1) When hive.metastore.disallow.incompatible.col.type.changes is true (the default) we
only allow StringFamily (STRING, CHAR, VARCHAR) conversion to a number that can hold the largest
numbers.  The theory being we don't want data loss you would get by converting the StringFamily
field into integers, etc.  In Hive version 2 the hierarchy of numbers had DECIMAL at the top.
 At some point during Hive ver 2 we realized this was incorrect and put DOUBLE the top.
> However, the Hive2 TypeInfoUtils.implicitConversion method allows StringFamily to either
DOUBLE or DECIMAL.
> The new org.apache.hadoop.hive.metastore.ColumnType class under hive version 3 hive-standalone-metadata-server
method checkColTypeChangeCompatible lost a version 2 series bug fix that drops CHAR/VARCHAR
(and DECIMAL I think) type decorations when checking for Schema Evolution compatibility.
> Hive1 version 2 did undecoratedTypeName(oldType) and Hive2 version performed the logic
in TypeInfoUtils.implicitConvertible on the PrimitiveCategory not the raw type string.



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