Oracle SQL function json_serialize takes JSON data (of any SQL data type, VARCHAR2, CLOB, or BLOB) as input and returns a textual representation of it (as VARCHAR2, CLOB, or BLOB data). VARCHAR2(4000) is the default return type.

You typically use json_serialize to transform the result of a query. It supports an error clause and a returning clause. You can specify pretty-printing for the result, and you can truncate the result to fit the return type.

Function json_serialize always produces JSON data that conforms to the JSON standard (RFC 4627). The returned data uses only the standard data types of the JSON language: object, array, and the scalar types string, number, Boolean, and null.

You can use json_serialize to convert binary JSON data to textual form (CLOB or VARCHAR2), or to transform textual JSON data by pretty-printing it or escaping non-ASCII Unicode characters in it. An important use case is serializing JSON data that is stored in a BLOB column. A BLOB result is in the AL32UTF8 character set. But whatever the data type returned by json_serialize, the returned data represents textual JSON data.

SELECT json_serialize(po_document PRETTY) FROM j_purchaseorder;