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https://issues.apache.org/jira/browse/FLINK-40978?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated FLINK-40978:
-----------------------------------
Labels: pull-request-available (was: )
> Cast from VARIANT through FromVariantConverter
> ----------------------------------------------
>
> Key: FLINK-40978
> URL: https://issues.apache.org/jira/browse/FLINK-40978
> Project: Flink
> Issue Type: Improvement
> Components: Table SQL / Planner, Table SQL / Runtime
> Affects Versions: 2.4.0
> Reporter: Ramin Gharib
> Assignee: Ramin Gharib
> Priority: Major
> Labels: pull-request-available
>
> Every \{{CAST(v AS T)}} from \{{VARIANT}} generates its own code today. Six
> planner cast rules each emit the walk for their target: primitives, ARRAY,
> ROW, MAP and character strings, plus a shared base class. For \{{CAST(v AS
> ARRAY<INT>)}} the generated code is:
> {code:java}
> int arraySize$2 = VariantCastUtils.arraySize(variant$1, "ARRAY<INT>");
> java.lang.Integer[] objArray$3 = new java.lang.Integer[arraySize$2];
> for (int i$4 = 0; i$4 < arraySize$2; i$4++) {
> Variant element$5 = variant$1.getElement(i$4);
> if (!element$5.isNull()) {
> result$6 = ((int) VariantCastUtils.toIntegral(element$5,
> -2147483648L, 2147483647L, "INTEGER"));
> objArray$3[i$4] = result$6;
> }
> }
> result$0 = new GenericArrayData(objArray$3);
> {code}
> The write side went the other way in FLINK-40826. \{{CAST(x AS VARIANT)}}
> calls a \{{ToVariantConverter}} in flink-table-common, built once per type.
> The read side has no such class. A format that reads a \{{VARIANT}} into SQL
> types cannot reuse the cast, and the null and shape rules are spread over
> several rules.
> h3. Proposal
> Add \{{FromVariantConverter}} to flink-table-common as the twin of
> \{{ToVariantConverter}}. It is built once per target type and returns
> internal data. The generated code shrinks to one call:
> {code:java}
> result$1 = ((ArrayData)(fromVariantConverter$2.convert(variant$0)));
> {code}
> * Merge the six read-side rules into one \{{FromVariantCastRule}}. Printing
> keeps its own path through \{{VariantCastUtils#toPrintString}}, because a
> printed value must never fail.
> * Move \{{VariantCastUtils}} from flink-table-runtime to flink-table-common.
> The converter calls it, and common cannot depend on runtime. The class is
> \{{@Internal}}.
> * Add \{{getSessionZoneId()}} to \{{CodeGeneratorCastRule.Context}}. The
> converter needs the zone when it is created. \{{CastRule.Context}} already
> exposes it.
> h3. Behavior
> No user-visible change. Every result, error message and null rule stays the
> same. Existing tests pass unchanged, apart from the rule names in
> \{{CastRuleProviderTest}}.
> Internal differences:
> * A \{{ROW}} result is a \{{GenericRowData}} instead of a \{{BinaryRowData}},
> because \{{BinaryRowWriter}} is not in common. A \{{VARIANT}} below a
> \{{ROW}} is still copied out of its parent.
> * An \{{ARRAY}} of a \{{NOT NULL}} primitive holds boxed values instead of a
> primitive array.
> * A primitive target boxes its value through the converter. The write side
> accepted the same cost.
> * A \{{DISTINCT}} target now casts like its source type. It used to fail
> during code generation. SQL cannot create such a type.
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