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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-5419) Calculate return string length for literals & some string functions
Date Thu, 27 Apr 2017 21:31:04 GMT

    [ https://issues.apache.org/jira/browse/DRILL-5419?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15987721#comment-15987721
] 

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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