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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 Fri, 12 May 2017 17:39:04 GMT

    [ https://issues.apache.org/jira/browse/DRILL-5419?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16008445#comment-16008445
] 

ASF GitHub Bot commented on DRILL-5419:
---------------------------------------

Github user jinfengni commented on the issue:

    https://github.com/apache/drill/pull/819
  
    I agreed with @paul-rogers  that BatchSchema and MaterializedField should consider all
fields (I once briefly mentioned to @paul-rogers I feel there might be bug in the equals/hashCode
methods). 
    
    Regarding Paul's 3 point, if we can get the schema infor (varchar length) from data, i.e.
the underneath storage plugin (RDBMS) provides such information, when Drill gets the batch
from recordReader, then Arina's patch will work the same way as as the input is a string literal.
In that sense, the work in this patch is complimentary to how we know the table column's varchar
length. 


> 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
>              Labels: ready-to-commit
>             Fix For: 1.11.0
>
>         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.
> *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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