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https://issues.apache.org/jira/browse/DRILL-5419?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15987721#comment-15987721
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ASF GitHub Bot commented on DRILL-5419:
---------------------------------------
Github user jinfengni commented on a diff in the pull request:
https://github.com/apache/drill/pull/819#discussion_r113762757
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/expr/annotations/FunctionTemplate.java
---
@@ -106,15 +106,21 @@
DECIMAL_ADD_SCALE,
DECIMAL_SET_SCALE,
DECIMAL_ZERO_SCALE,
- SC_BOOLEAN_OPERATOR
+ SC_BOOLEAN_OPERATOR,
--- End diff --
I feel we probably overuse the concept of FunctionScope. The original
intention, in my view, is to specify one function could be used in a context
for aggregate (n -> 1 ) or simple (1 -> 1). Starting from the decimal
functions, we add more possibilities of FunctionScope, while all those new
possibilities are for different ways of inferring return types. In stead of
keeping adding more for those string functions, can we probably add a new
annotation to function template, to denote the return type infer logic for
different functions? I feel that the code might be cleaner.
On the other hand, I'm fine if we leave it as it is, since the new string
functions are following existing approach, and may choose to revisit this later
on.
> Calculate return string length for literals & some string functions
> -------------------------------------------------------------------
>
> Key: DRILL-5419
> URL: https://issues.apache.org/jira/browse/DRILL-5419
> Project: Apache Drill
> Issue Type: Bug
> Affects Versions: 1.9.0
> Reporter: Arina Ielchiieva
> Assignee: Arina Ielchiieva
> Attachments: version_with_cast.JPG
>
>
> Though Drill is schema-less and cannot determine in advance what the length
> of the column should be but if query has an explicit type/length specified,
> Drill should return correct column length.
> For example, JDBC / ODBC Driver is ALWAYS returning 64K as the length of a
> varchar or char even if casts are applied.
> Changes:
> *LITERALS*
> String literals length is the same as actual literal length.
> Example: for 'aaa' return length is 3.
> *CAST*
> Return length is the one indicated in cast expression. This also applies when
> user has created view where each string columns was casted to varchar with
> some specific length.
> This length will be returned to the user without need to apply cast one more
> time. Below mentioned functions can take leverage of underlying varchar
> length and calculate return length.
> *LOWER, UPPER, INITCAP, REVERSE, FIRST_VALUE, LAST_VALUE*
> Return length is underlying column length, i.e. if column is known, the same
> length will be returned.
> Example:
> lower(cast(col as varchar(30))) will return 30.
> lower(col) will return max varchar length, since we don't know actual column
> length.
> *LAG, LEAD*
> Return length is underlying column length but column type will be nullable.
> *LPAD, RPAD*
> Pads the string to the length specified. Return length is this specified
> length.
> *CONCAT, CONCAT OPERATOR (||)*
> Return length is sum of underlying columns length. If length is greater then
> varchar max length, varchar max length is returned.
> *SUBSTR, SUBSTRING, LEFT, RIGHT*
> Calculates return length according to each function substring rules, for
> example, taking into account how many char should be substracted.
> *IF EXPRESSIONS (CASE STATEMENT, COALESCE), UNION OPERATOR*
> When combining string columns with different length, return length is max
> from source columns.
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