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https://issues.apache.org/jira/browse/CASSANDRA-18647?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andres de la Peña updated CASSANDRA-18647:
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Status: Ready to Commit (was: Review In Progress)
> CASTing a float to decimal adds wrong digits
> --------------------------------------------
>
> Key: CASSANDRA-18647
> URL: https://issues.apache.org/jira/browse/CASSANDRA-18647
> Project: Cassandra
> Issue Type: Bug
> Components: CQL/Semantics
> Reporter: Nadav Har'El
> Assignee: Stefan Miklosovic
> Priority: Normal
> Fix For: 5.x
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> If I create a table with a *float* (32-bit) column, and cast it to the
> *decimal* type, the casting wrongly passes through the double (64-bit) type
> and picks up extra, wrong, digits. For example, if we have a column e of type
> "float", and run
> INSERT INTO tbl (p, e) VALUES (1, 5.2)
> SELECT CAST(e AS decimal) FROM tbl WHERE p=1
> The result is the "decimal" value 5.199999809265137, with all those extra
> wrong digits. It would have been better to get back the decimal value 5.2,
> with only two significant digits.
> It appears that this happens because Cassandra's implementation first
> converts the 32-bit float into a 64-bit double, and only then converts that -
> with all the silly extra digits it picked up in the first conversion - into a
> "decimal" value.
> Contrast this with CAST(e AS text) which works correctly - it returns the
> string "5.2" - only the actual digits of the 32-bit floating point value are
> converted to the string, without inventing additional digits in the process.
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