[IMPALA-4936] Cast from double to decimal doesn't always handle overflow correctly

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: Impala 2.9.0
• Fix Version/s: Impala 2.9.0
• Component/s: Backend
• Labels: correctness
• Epic Link: Numeric Datatype Conversions
• Assignee: Zach Amsden
• Reporter: Michael Ho
• Created: 15/Feb/17 01:23
• Updated: 14/Mar/17 18:36
• Resolved: 24/Feb/17 19:43

Description

Casting from a double value which will overflow the maximum decimal type should return NULL. It doesn't appear to work as expected all the time when casting from double to decimal when the input value is too large.

[localhost:21000] > select typeof(555555555555555555555555555555555555555);
Query: select typeof(555555555555555555555555555555555555555)
+-------------------------------------------------+
| typeof(555555555555555555555555555555555555555) |
+-------------------------------------------------+
| DOUBLE                                          |
+-------------------------------------------------+
Fetched 1 row(s) in 0.01s

[localhost:21000] > select cast(555555555555555555555555555555555555555 as DECIMAL(38,0));
Query: select cast(555555555555555555555555555555555555555 as DECIMAL(38,0))
+----------------------------------------------------------------+
| cast(555555555555555555555555555555555555555 as decimal(38,0)) |
+----------------------------------------------------------------+
| 0                                                              |
+----------------------------------------------------------------+
Fetched 1 row(s) in 0.01s

It seems to work fine if we are within certain bounds:

[localhost:21000] > select cast(123456789012345678901234567890123456789 as DECIMAL(38,0));
Query: select cast(123456789012345678901234567890123456789 as DECIMAL(38,0))
+----------------------------------------------------------------+
| cast(123456789012345678901234567890123456789 as decimal(38,0)) |
+----------------------------------------------------------------+
| NULL                                                           |
+----------------------------------------------------------------+
WARNINGS: UDF WARNING: Expression overflowed, returning NULL

Fetched 1 row(s) in 0.01s

Casting from string seems to work fine:

[localhost:21000] > select cast('555555555555555555555555555555555555555' as DECIMAL(38,0));
Query: select cast('555555555555555555555555555555555555555' as DECIMAL(38,0))
+------------------------------------------------------------------+
| cast('555555555555555555555555555555555555555' as decimal(38,0)) |
+------------------------------------------------------------------+
| NULL                                                             |
+------------------------------------------------------------------+
Fetched 1 row(s) in 0.01s