Nadav Har'El created CASSANDRA-18647:
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Summary: 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
Reporter: Nadav Har'El
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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