Vladimir Steshin created IGNITE-24336:
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             Summary: Calcite. Add support of user-defined table functions.
                 Key: IGNITE-24336
                 URL: https://issues.apache.org/jira/browse/IGNITE-24336
             Project: Ignite
          Issue Type: Improvement
            Reporter: Vladimir Steshin
            Assignee: Vladimir Steshin


We should implement user-defined table functions. They also have a 
implementation in Calcite, `_TableFunctionImpl_`. And we also have user-defined 
scalar functions.

Table functions should be described similarly to the existing configuration of 
scalar functions, via `_CacheConfiguration#setSqlFunctionClasses()_` and 
annotation `_@QuerySqlTableFunction_`. Or we might use another annotation. The 
annotation should describe the returned columns and their data types.

Example:
{code:java}
public static final class IncorrectTableFunctionsLibrary {
    @QuerySqlFunction(tableColumnTypes = {Integer.class, String.class}, 
tableColumnNames = {"INT_COL", "STR_COL"})

    public static Iterable duplicateColumnName(int i, String s) {
        return Arrays.asList(
            Arrays.asList(i, s + i),
            Arrays.asList(i * 10, s + (i * 10))
        );
    }
}
{code}

Table function implementation must return an `Iterable` representing table 
rows. Each its element is an `_Object[]_` or an `_Iterable_` representing a 
table row. The number of row elements must match the number of the defined 
columns. 

*Known limitations*:
Only _Calcite_ engine will support table functions first.



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