TO_JSON and PARSE_JSON

The functions TO_JSON and PARSE_JSON in Snowflake are used for handling JSON data, but they serve different purposes.

TO_JSON

• Purpose: Converts a Snowflake SQL data type into its JSON representation.

• Usage: Typically used when you want to serialize data from a Snowflake table into a JSON string format.

• Example:
  This would output:

  SELECT TO_JSON(OBJECT_CONSTRUCT('key1', 'value1', 'key2', 'value2')) AS json_output;

  {"key1":"value1","key2":"value2"}

PARSE_JSON

• Purpose: Converts a string containing JSON data into a Snowflake VARIANT data type, which allows for querying JSON data.

• Usage: Used when you want to deserialize a JSON string into a format that can be queried using SQL.

• Example:
  This converts the JSON string into a
  VARIANT type, allowing you to query it like:

  SELECT PARSE_JSON('{"key1":"value1","key2":"value2"}') AS variant_output;

  SELECT variant_output:key1 FROM (SELECT PARSE_JSON('{"key1":"value1","key2":"value2"}') AS variant_output);

Key Differences:

1. Functionality:
   • TO_JSON: Converts structured data (like objects or arrays) to JSON string format.
   • PARSE_JSON: Converts JSON string data to Snowflake’s VARIANT data type, enabling JSON data querying.
2. Direction:
   • TO_JSON: Serialization (Structured data to JSON string).
   • PARSE_JSON: Deserialization (JSON string to VARIANT).
3. Use Cases:
   • TO_JSON: When you need to generate a JSON string from table data for storage, export, or API interactions.
   • PARSE_JSON: When you need to load and query JSON data from strings stored in tables.

Practical Example:

Suppose you have a table users with columns id, name, and attributes (where attributes is a JSON string).

• Using **TO_JSON**:

  SELECT id, name, TO_JSON(attributes) AS json_attributes
  FROM users;

  This converts the attributes column to a JSON string.

• Using **PARSE_JSON**:

  SELECT id, name, PARSE_JSON(attributes) AS parsed_attributes
  FROM users;

  This converts the JSON string in the attributes column to a VARIANT type, allowing JSON querying:

  SELECT id, name, parsed_attributes:key1
  FROM (SELECT id, name, PARSE_JSON(attributes) AS parsed_attributes FROM users);

In summary, use TO_JSON to convert data to JSON strings and PARSE_JSON to convert JSON strings to a queryable VARIANT type in Snowflake.