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https://issues.apache.org/jira/browse/CASSANDRA-14170?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16365287#comment-16365287
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Benjamin Lerer commented on CASSANDRA-14170:
--------------------------------------------
[~danfiala] Thanks for reporting the problem.
I pushed a branch
[here|https://github.com/apache/cassandra/compare/cassandra-3.11...blerer:14170-3.11]
to fix the problem and add some extra tests.
The patch can be merge without trouble into trunk and the Unit tests runs fine
on both branches. We do not have DTests for the {{CAST}} operations.
[~adelapena] Could you review?
> Loss of digits when doing CAST from varint/bigint to decimal
> ------------------------------------------------------------
>
> Key: CASSANDRA-14170
> URL: https://issues.apache.org/jira/browse/CASSANDRA-14170
> Project: Cassandra
> Issue Type: Bug
> Environment: Tested with Cassandra 3.11.1 but this issue is present
> since the implementation of cast functions.
> Reporter: Daniel Fiala
> Assignee: Benjamin Lerer
> Priority: Minor
>
> Cast functions from numeric types to decimal type are implemented as
> conversion to double first and then from double to decimal:
> [https://github.com/apache/cassandra/compare/trunk...blerer:10310-3.0#diff-6aa4a8f76df6c30c5bb4026b8c9251eeR80].
> This can cause loss of digits for big values stored in varint or bigint. It
> is probably unexpected because decimal can store such values precisely.
> Examples:
> {{cqlsh> CREATE TABLE cast_bigint_test(k int PRIMARY KEY, bigint_clmn
> bigint);}}
> {{cqlsh> INSERT INTO cast_bigint_test(k, decimal_clmn) VALUES(2,
> 9223372036854775807);}}
> {{cqlsh> SELECT CAST(bigint_clmn AS decimal) FROM cast_bigint_test;}}
> {{cast(bigint_clmn as decimal)}}
> {{------------------------------}}
> {{9.223372036854776E+18}}
> {{(1 rows)}}
> {{cqlsh> CREATE TABLE cast_varint_test (k int PRIMARY KEY, varint_clmn
> varint);}}
> {{cqlsh> INSERT INTO cast_varint_test(k, varint_clmn) values(2,
> 1234567890123456789);}}
> {{cqlsh> SELECT CAST(varint_clmn AS decimal) FROM cast_varint_test;}}
> {{cast(varint_clmn as decimal)}}
> {{------------------------------}}
> 1.23456789012345677E+18
> {{(1 rows)}}
>
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