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https://issues.apache.org/jira/browse/SPARK-30203?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Kent Yao resolved SPARK-30203.
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Resolution: Not A Problem
There is no UDCF in Spark
> store assignable if there exists an appropriate user-defined cast function
> --------------------------------------------------------------------------
>
> Key: SPARK-30203
> URL: https://issues.apache.org/jira/browse/SPARK-30203
> Project: Spark
> Issue Type: Sub-task
> Components: SQL
> Affects Versions: 3.0.0
> Reporter: Kent Yao
> Priority: Major
>
> h3. 9.2 Store assignment
> h4. Syntax Rules
> 1) Let T be the TARGET and let V be the VALUE in an application of the Syntax
> Rules of this Subclause.
> 2) Let TD and SD be the declared types of T and V, respectively.
> 3) If TD is character string, binary string, numeric, boolean, datetime,
> interval, or a user-defined type, then
> either SD shall be assignable to TD or there shall exist an appropriate
> user-defined cast function UDCF
> from SD to TD.
> _NOTE 319 — “Appropriate user-defined cast function” is defined in Subclause
> 4.11, “Data conversions”_
> h3. 4.11 Data conversions
> Implicit type conversion can occur in expressions, fetch operations, single
> row select operations, inserts, deletes,
> and updates. Explicit type conversions can be specified by the use of the
> CAST operator.
>
> The current implementation for ANSI store assignment is totally out of
> context.
> According to this rule, `there shall exist an appropriate user-defined cast
> function UDCF`, the spark legacy store assignment is just fine because we do
> have *appropriate cast* _*functions.*_
> At least according to the ansi cast rule, the current ANSI assignment policy
> is too strict to the ANSI cast rules
>
> {code:java}
> * (SD) --------------------- (TD) -------------------------
> * | EN AN C D T TS YM DT BO UDT B RT CT RW
> * EN | Y Y Y N N N M M N M N M N N
> * AN | Y Y Y N N N N N N M N M N N
> * C | Y Y Y Y Y Y Y Y Y M N M N N
> * D | N N Y Y N Y N N N M N M N N
> * T | N N Y N Y Y N N N M N M N N
> * TS | N N Y Y Y Y N N N M N M N N
> * YM | M N Y N N N Y N N M N M N N
> * DT | M N Y N N N N Y N M N M N N
> * BO | N N Y N N N N N Y M N M N N
> * UDT | M M M M M M M M M M M M M N
> * B | N N N N N N N N N M Y M N N
> * RT | M M M M M M M M M M M M N N
> * CT | N N N N N N N N N M N N M N
> * RW | N N N N N N N N N N N N N M
> *
> * Where:
> * EN = Exact Numeric
> * AN = Approximate Numeric
> * C = Character (Fixed- or Variable-Length, or Character Large Object)
> * D = Date
> * T = Time
> * TS = Timestamp
> * YM = Year-Month Interval
> * DT = Day-Time Interval
> * BO = Boolean
> * UDT = User-Defined Type
> * B = Binary (Fixed- or Variable-Length or Binary Large Object)
> * RT = Reference type
> * CT = Collection type
> * RW = Row type
> {code}
>
>
> _cc [~cloud_fan] [~gengliang]_ [~maropu]
>
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