Result JSON unsupported types

[gruuya]

Arrow JSON writer that we use to format the output result of queries does not support all data types that Datafusion handles. For example:

$ curl -H "Content-Type: application/json" http://localhost:8080/q -d@-<<EOF
{"query": "CREATE TABLE test_table(dec_column NUMERIC, float_column REAL); SELECT column_name, data_type FROM information_schema.columns WHERE table_name = 'test_table'"}
EOF
{"column_name":"dec_column","data_type":"Decimal128(38, 10)"}
{"column_name":"float_column","data_type":"Float32"}
$ curl -H "Content-Type: application/json" http://localhost:8080/q -d@-<<EOF
{"query": "INSERT INTO test_table (float_column) VALUES (42.0); SELECT * FROM test_table"}
EOF
Arrow error: Json error: data type Decimal128(38, 10) not supported in nested map for json writer