You can't do this directly with BigQuery, but you can make it work in two passes:
(1) Import your JSON data as a CSV file with a single string column.
(2) Transform each row to pack your "any-type" field into a string. Write a UDF that takes a string and emits the final set of columns you would like. Append the output of this query to your target table.
Example
I'll start with some JSON:
{"a": 0, "b": "zero", "c": { "woodchuck": "a"}}
{"a": 1, "b": "one", "c": { "chipmunk": "b"}}
{"a": 2, "b": "two", "c": { "squirrel": "c"}}
{"a": 3, "b": "three", "c": { "chinchilla": "d"}}
{"a": 4, "b": "four", "c": { "capybara": "e"}}
{"a": 5, "b": "five", "c": { "housemouse": "f"}}
{"a": 6, "b": "six", "c": { "molerat": "g"}}
{"a": 7, "b": "seven", "c": { "marmot": "h"}}
{"a": 8, "b": "eight", "c": { "badger": "i"}}
Import it into BigQuery as a CSV with a single STRING column (I called it 'blob'). I had to set the delimiter character to something arbitrary and unlikely (thorn -- 'þ') or it tripped over the default ','.
Verify your table imported correctly. You should see your simple one-column schema and the preview should look just like your source file.
Next, we write a query to transform it into your desired shape. For this example, we'd like the following schema:
a (INTEGER)
b (STRING)
c (STRING -- packed JSON)
We can do this with a UDF:
// Map a JSON string column ('blob') => { a (integer), b (string), c (json-string) }
bigquery.defineFunction(
'extractAndRepack', // Name of the function exported to SQL
['blob'], // Names of input columns
[{'name': 'a', 'type': 'integer'}, // Output schema
{'name': 'b', 'type': 'string'},
{'name': 'c', 'type': 'string'}],
function (row, emit) {
var parsed = JSON.parse(row.blob);
var repacked = JSON.stringify(parsed.c);
emit({a: parsed.a, b: parsed.b, c: repacked});
}
);
And a corresponding query:
SELECT a, b, c FROM extractAndRepack(JsonAnyKey.raw)
Now you just need to run the query (selecting your desired target table) and you'll have your data in the form you like.
Row a b c
1 0 zero {"woodchuck":"a"}
2 1 one {"chipmunk":"b"}
3 2 two {"squirrel":"c"}
4 3 three {"chinchilla":"d"}
5 4 four {"capybara":"e"}
6 5 five {"housemouse":"f"}
7 6 six {"molerat":"g"}
8 7 seven {"marmot":"h"}
9 8 eight {"badger":"i"}
