Aaron Davidson created SPARK-21513:
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Summary: SQL to_json should support all column types
Key: SPARK-21513
URL: https://issues.apache.org/jira/browse/SPARK-21513
Project: Spark
Issue Type: Improvement
Components: SQL
Affects Versions: 2.2.0
Reporter: Aaron Davidson
The built-in SQL UDF "to_json" currently supports serializing StructType
columns, as well as Arrays of StructType columns. If you attempt to use it on a
different type, for example a map, you get an error like this:
{code}
AnalysisException: cannot resolve 'structstojson(`tags`)' due to data type
mismatch: Input type map<string,string> must be a struct or array of structs.;;
{code}
This limitation seems arbitrary; if I were to go through the effort of
enclosing my map in a struct, it would be serializable. Same thing with any
other non-struct type.
Therefore the desired improvement is to allow to_json to operate directly on
any column type. The associated code is
[here](https://github.com/apache/spark/blob/86174ea89b39a300caaba6baffac70f3dc702788/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/jsonExpressions.scala#L653).
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