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https://issues.apache.org/jira/browse/IMPALA-8367?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16842123#comment-16842123
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Tamas Mate commented on IMPALA-8367:
------------------------------------
[~tarmstrong], I have checked the Hive behavior, it uses
[SimpleDateFormat|https://github.com/cloudera/hive/blob/trunk/ql/src/java/org/apache/hadoop/hive/ql/udf/UDFFromUnixTime.java#L121]
to resolve the format and 'u' is the day number of the week. While MySQL
behaves a bit differently, it goes with NULL if the value is null, otherwise it
prints the unknown format.
{code:sql}
SELECT FROM_UNIXTIME(NULL, 'u');
+--------------------------+
| FROM_UNIXTIME(NULL, 'u') |
+--------------------------+
| NULL |
+--------------------------+
SELECT FROM_UNIXTIME(123, 'u');
+-------------------------+
| FROM_UNIXTIME(123, 'u') |
+-------------------------+
| u |
+-------------------------+
{code}
Should we go with the following or should we think about implementing the Hive
behavior?
- SELECT FROM_UNIXTIME(NULL, 'u'); -> NULL
- SELECT FROM_UNIXTIME(123, 'u'); -> Fail the query with "Bad date/time
conversion format: u"
> from_unixtime Bad date/time conversion format: u on NULL value
> --------------------------------------------------------------
>
> Key: IMPALA-8367
> URL: https://issues.apache.org/jira/browse/IMPALA-8367
> Project: IMPALA
> Issue Type: Bug
> Components: Backend
> Affects Versions: Impala 2.11.0
> Environment: impalad version 2.11.0-cdh5.14.2 RELEASE (build
> ed85dce709da9557aeb28be89e8044947708876c) Built on Tue Mar 27 13:39:48 PDT
> 2018
> Reporter: Sergio Leoni
> Assignee: Tamas Mate
> Priority: Minor
> Labels: newbie, ramp-up
>
> The function
> {code:sql}
> from_unixtime(bigint unixtime[, string format]) {code}
> output error if the value of unixtime is NULL and format is 'u'.
>
> This doesn't work:
> {code:sql}
> SELECT FROM_UNIXTIME(NULL, 'u')
> {code}
> {noformat}
> Bad date/time conversion format: u{noformat}
>
> This works:
> {code:sql}
> SELECT FROM_UNIXTIME(NULL, 'yyyy-MM-dd')
> {code}
> {noformat}
> |from_unixtime(null, 'yyyy-mm-dd')|
> |---------------------------------|
> | NULL |
> |---------------------------------|{noformat}
>
> I haven't checked all the possible combinations.
> Other software like Hive handles this correctly.
>
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