Question 108954 in Json Question posted in
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JSON array to rows in ClickHouse

What query would transpose the following JSON value to multiple rows. Examples with nested JSON objects are sparse.

[{"a":{"b":"val", "c":1}},{"a":{"b":"val", "c":4}}]

Tried combinations of JSONExtract but having difficulty with nested object

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2

Answers


  2. 0

    You can use JSONEachRow format to read an array of objects. Nested object ("a" : {…}) can be read into:

    1. String and than be parsed it using JSONExtract:
    :) select * from format(JSONEachRow, 'a String', '[{"a":{"b":"val", "c":1}},{"a":{"b":"val", "c":4}}]')

┌─a──────────────────┐
│ {"b":"val", "c":1} │
│ {"b":"val", "c":4} │
└────────────────────┘

 :) select JSONExtractString(a, 'b') from format(JSONEachRow, 'a String', '[{"a":{"b":"val", "c":1}},{"a":{"b":"val", "c":4}}]')


┌─JSONExtractString(a, 'b')─┐
│ val                       │
│ val                       │
└───────────────────────────┘
    1. Named tuple (if all nested objects are known or you want to read only some of them):
    avogar-dev :) select * from format(JSONEachRow, 'a Tuple(b String, c UInt32)', '[{"a":{"b":"val", "c":1}},{"a":{"b":"val", "c":4}}]')

┌─a─────────┐
│ ('val',1) │
│ ('val',4) │
└───────────┘
    1. Using experimental JSON object type:
     :) select * from format(JSONEachRow, 'a JSON', '[{"a":{"b":"val", "c":1}},{"a":{"b":"val", "c":4}}]') settings allow_experimental_object_type=1

┌─a─────────────────┐
│ {"b":"val","c":1} │
│ {"b":"val","c":4} │
└───────────────────┘

    Note: JSON type is still experimental and using it can lean to unexpected bugs.

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