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https://issues.apache.org/jira/browse/DRILL-5419?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15987738#comment-15987738
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ASF GitHub Bot commented on DRILL-5419:
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Github user jinfengni commented on the issue:
https://github.com/apache/drill/pull/819
2 additional comments.
1. Maybe we need include the length field in MaterializedField.toString()
for varchar type if length is set.
2. Will a varchar(5) vs varchar(10) be regarded as schema change? The
underneath value vector would be same. Not sure if we may see more schema
change exception. I tried to come up with some example, but could not find one.
It may be worthwhile to think it over.
> 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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