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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=15987723#comment-15987723
] 

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_r113802524
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/planner/sql/TypeInferenceUtils.java
---
    @@ -394,31 +414,37 @@ public RelDataType inferReturnType(SqlOperatorBinding opBinding)
{
       }
     
       private static class DrillConcatSqlReturnTypeInference implements SqlReturnTypeInference
{
    -    private static final DrillConcatSqlReturnTypeInference INSTANCE = new DrillConcatSqlReturnTypeInference();
    --- End diff --
    
    For the various SqlReturnTypeInference, seems the same logic is applied here and in DrillConcatFuncHolder.
 If we choose not to expand "FunctionScope" and model it as ReturnTypeInference, then we probably
will be able to abstract and share the common code. That would save effort in the future to
maintain two almost identical pieces of codes. 


> 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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