CODEWITHSUNDEEP
javasqlapache-flinkflink-sql
huiwen.zheng
huiwen.zheng

Reputation: 19

how to cast multiset datatype to string in flink sql?

when i was doing such query in flink sql:

    SELECT COLLECT(col1) OVER (
        PARTITION BY col2
        ORDER BY col3
        ROWS BETWEEN 1 PRECEDING AND CURRENT ROW
    ) AS col4
    FROM table

how can i cast the col4, which is a multiset datatype, to string?

i have tried cast(col4 as string), but it didnt work. the exception is Cast function cannot convert value of type BIGINT MULTISET to type VARCHAR(2147483647)

OR how can i pass the multiset data to a java udf and then trasform to a string? how to write such udf?

Upvotes: 1

Views: 2106

Answers (2)

matriv
matriv

Reputation: 1

There is also another open issue actively worked on, which has to do with supporting of printing but also casting all the structured types to STRING

Upvotes: 0

twalthr
twalthr

Reputation: 2664

Currently, casting of multisets is limited. The community is currently working on improving this.

Until then, I would recommend to use a scalar function. UDFs can accept all types. Since the automatic reflection logic reserves the Map class for the MAP type. You have to add a type hint.

public class MultisetToString extends ScalarFunction {

  public String eval(@DataTypeHint("MULTISET<STRING>") Map<String, Integer> multiset) {
    return multiset.toString();
  }
}

Upvotes: 3

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