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User Guide

Extracting Data from JSON

You may have source data with containing JSON-encoded strings that you do not necessarily want to deserialize into a table in Athena. In this case, you can still run SQL operations on this data, using the JSON functions available in Presto.

Consider this JSON string as an example dataset.

{"name": "Susan Smith", "org": "engineering", "projects": [ {"name":"project1", "completed":false}, {"name":"project2", "completed":true} ] }

Examples: extracting properties

To extract the name and projects properties from the JSON string, use the json_extract function as in the following example. The json_extract function takes the column containing the JSON string, and searches it using a JSONPath-like expression with the dot . notation.

Note

JSONPath performs a simple tree traversal. It uses the $ sign to denote the root of the JSON document, followed by a period and an element nested directly under the root, such as $.name.

WITH dataset AS ( SELECT '{"name": "Susan Smith", "org": "engineering", "projects": [{"name":"project1", "completed":false}, {"name":"project2", "completed":true}]}' AS blob ) SELECT json_extract(blob, '$.name') AS name, json_extract(blob, '$.projects') AS projects FROM dataset

The returned value is a JSON-encoded string, and not a native Athena data type.

+-----------------------------------------------------------------------------------------------+ | name | projects | +-----------------------------------------------------------------------------------------------+ | "Susan Smith" | [{"name":"project1","completed":false},{"name":"project2","completed":true}] | +-----------------------------------------------------------------------------------------------+

To extract the scalar value from the JSON string, use the json_extract_scalar function. It is similar to json_extract, but returns only scalar values (Boolean, number, or string).

Note

Do not use the json_extract_scalar function on arrays, maps, or structs.

WITH dataset AS ( SELECT '{"name": "Susan Smith", "org": "engineering", "projects": [{"name":"project1", "completed":false},{"name":"project2", "completed":true}]}' AS blob ) SELECT json_extract_scalar(blob, '$.name') AS name, json_extract_scalar(blob, '$.projects') AS projects FROM dataset

This query returns:

+---------------------------+ | name | projects | +---------------------------+ | Susan Smith | | +---------------------------+

To obtain the first element of the projects property in the example array, use the json_array_get function and specify the index position.

WITH dataset AS ( SELECT '{"name": "Bob Smith", "org": "engineering", "projects": [{"name":"project1", "completed":false},{"name":"project2", "completed":true}]}' AS blob ) SELECT json_array_get(json_extract(blob, '$.projects'), 0) AS item FROM dataset

It returns the value at the specified index position in the JSON-encoded array.

+---------------------------------------+ | item | +---------------------------------------+ | {"name":"project1","completed":false} | +---------------------------------------+

To return an Athena string type, use the [] operator inside a JSONPath expression, then Use the json_extract_scalar function. For more information about [], see Accessing Array Elements.

WITH dataset AS ( SELECT '{"name": "Bob Smith", "org": "engineering", "projects": [{"name":"project1", "completed":false},{"name":"project2", "completed":true}]}' AS blob ) SELECT json_extract_scalar(blob, '$.projects[0].name') AS project_name FROM dataset

It returns this result:

+--------------+ | project_name | +--------------+ | project1 | +--------------+