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https://issues.apache.org/jira/browse/KYLIN-5756?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17830479#comment-17830479
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pengfei.zhan commented on KYLIN-5756:
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h1. Fix design
# When generating java code in calcite, to determine whether the + operator
needs to be converted to plus() or whether to directly use addition in java,
add a condition that when the parameters on both sides of the plus operator are
of string type or numeric type, plus() is used directly.
i.e. fix the '1' + 3 + '3' in the previous sql, the java code is plus('1' + 3)
+ '3'.
After the fix it is plus(plus('1' + 3), '3')
# Changed the return value of the custom plus function in calcite from Double
to bigDecimal. The reasons are as follows:
* Constant folding by calcite to generate java code derives whether it is
isNullable, if the RexCall with its nullable is false, it will automatic
unboxing;
* The expression 'a' + 3 is considered to be non-nullable by calcite, because
the two arguments are constants and neither of them is null, so the whole thing
is considered non-null;
* In spark, 'a' + 3 results in null, so our implementation of the plus method
gives the same result
* In summary, when expression `plus(string, number)` returns Double, the java
code for `'a' + 3 + '3' ` is actually `plus(plus('a' + 3).doubleValue(), '3')`,
which then throws an NPE when the calculation is performed.
This behavior change of isNullable involves a wide range, and it is dangerous
to modify it directly, so we changed the return value of plus operator to
BigDecimal to avoid unboxing.
> Concat string and number with '+' gives unexpected result
> ---------------------------------------------------------
>
> Key: KYLIN-5756
> URL: https://issues.apache.org/jira/browse/KYLIN-5756
> Project: Kylin
> Issue Type: Improvement
> Components: Query Engine
> Affects Versions: 5.0-beta
> Reporter: pengfei.zhan
> Assignee: pengfei.zhan
> Priority: Major
> Fix For: 5.0-beta
>
>
> Concat string and number gives unexpected result.
> For example:
> 1. concat constant with plus operator, gives unexpected result
> {code:java}
> 1' + 3 + 3 // 7 (correct)
> '1' + 3 + '3' // 4.03 (wrong result)
> '1' + '3' + 'a' // error
> {code}
> 2. concat string and number, the first '+' produces null
> {code:java}
> 'q' + 1 + 1 // error
> {code}
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