12.17.4 Functions That Modify JSON Values

JSON_ARRAY_APPEND(json_doc, path, val[, path, val] ...)

Appends values to the end of the indicated arrays within a JSON document and returns the result. Returns NULL if any argument is NULL. An error occurs if the json_doc argument is not a valid JSON document or any path argument is not a valid path expression or contains a * or ** wildcard.

The path-value pairs are evaluated left to right. The document produced by evaluating one pair becomes the new value against which the next pair is evaluated.

If a path selects a scalar or object value, that value is autowrapped within an array and the new value is added to that array. Pairs for which the path does not identify any value in the JSON document are ignored.

In MySQL 5.7, this function was named JSON_APPEND(). That name is no longer supported in MySQL 8.0.

JSON_ARRAY_INSERT(json_doc, path, val[, path, val] ...)

Updates a JSON document, inserting into an array within the document and returning the modified document. Returns NULL if any argument is NULL. An error occurs if the json_doc argument is not a valid JSON document or any path argument is not a valid path expression or contains a * or ** wildcard or does not end with an array element identifier.

The path-value pairs are evaluated left to right. The document produced by evaluating one pair becomes the new value against which the next pair is evaluated.

Pairs for which the path does not identify any array in the JSON document are ignored. If a path identifies an array element, the corresponding value is inserted at that element position, shifting any following values to the right. If a path identifies an array position past the end of an array, the value is inserted at the end of the array.

Earlier modifications affect the positions of the following elements in the array, so subsequent paths in the same JSON_ARRAY_INSERT() call should take this into account. In the final example, the second path inserts nothing because the path no longer matches anything after the first insert.

JSON_INSERT(json_doc, path, val[, path, val] ...)

Inserts data into a JSON document and returns the result. Returns NULL if any argument is NULL. An error occurs if the json_doc argument is not a valid JSON document or any path argument is not a valid path expression or contains a * or ** wildcard.

The path-value pairs are evaluated left to right. The document produced by evaluating one pair becomes the new value against which the next pair is evaluated.

A path-value pair for an existing path in the document is ignored and does not overwrite the existing document value. A path-value pair for a nonexisting path in the document adds the value to the document if the path identifies one of these types of values:

Otherwise, a path-value pair for a nonexisting path in the document is ignored and has no effect.

For a comparison of JSON_INSERT(), JSON_REPLACE(), and JSON_SET(), see the discussion of JSON_SET().

The third and final value listed in the result is a quoted string and not an array like the second one (which is not quoted in the output); no casting of values to the JSON type is performed. To insert the array as an array, you must perform such casts explicitly, as shown here:

JSON_MERGE(json_doc, json_doc[, json_doc] ...)

Merges two or more JSON documents. Synonym for JSON_MERGE_PRESERVE(); deprecated in MySQL 8.0.3 and subject to removal in a future release.

For additional examples, see the entry for JSON_MERGE_PRESERVE().

JSON_MERGE_PATCH(json_doc, json_doc[, json_doc] ...)

Performs an RFC 7396 compliant merge of two or more JSON documents and returns the merged result, without preserving members having duplicate keys. Raises an error if at least one of the documents passed as arguments to this function is not valid.

JSON_MERGE_PATCH() performs a merge as follows:

For additional information, see Normalization, Merging, and Autowrapping of JSON Values.

You can use this function to remove a member by specifying null as the value of the same member in the seond argument, as shown here:

This example shows that the function operates in a recursive fashion; that is, values of members are not limited to scalars, but rather can themselves be JSON documents:

JSON_MERGE_PATCH() is supported in MySQL 8.0.3 and later.

JSON_MERGE_PATCH() compared with JSON_MERGE_PRESERVE().  The behavior of JSON_MERGE_PATCH() is the same as that of JSON_MERGE_PRESERVE(), with the following two exceptions:

This example compares the results of merging the same 3 JSON objects, each having a matching key "a", with each of these two functions:

JSON_MERGE_PRESERVE(json_doc, json_doc[, json_doc] ...)

Merges two or more JSON documents and returns the merged result. Returns NULL if any argument is NULL. An error occurs if any argument is not a valid JSON document.

Merging takes place according to the following rules. For additional information, see Normalization, Merging, and Autowrapping of JSON Values.

This function was added in MySQL 8.0.3 as a synonym for JSON_MERGE(). The JSON_MERGE() function is now deprecated, and is subject to removal in a future release of MySQL.

This function is similar to but differs from JSON_MERGE_PATCH() in significant respects; see JSON_MERGE_PATCH() compared with JSON_MERGE_PRESERVE(), for more information.

JSON_REMOVE(json_doc, path[, path] ...)

Removes data from a JSON document and returns the result. Returns NULL if any argument is NULL. An error occurs if the json_doc argument is not a valid JSON document or any path argument is not a valid path expression or is $ or contains a * or ** wildcard.

The path arguments are evaluated left to right. The document produced by evaluating one path becomes the new value against which the next path is evaluated.

It is not an error if the element to be removed does not exist in the document; in that case, the path does not affect the document.

JSON_REPLACE(json_doc, path, val[, path, val] ...)

Replaces existing values in a JSON document and returns the result. Returns NULL if any argument is NULL. An error occurs if the json_doc argument is not a valid JSON document or any path argument is not a valid path expression or contains a * or ** wildcard.

The path-value pairs are evaluated left to right. The document produced by evaluating one pair becomes the new value against which the next pair is evaluated.

A path-value pair for an existing path in the document overwrites the existing document value with the new value. A path-value pair for a nonexisting path in the document is ignored and has no effect.

In MySQL 8.0.4, the optimizer can perform a partial, in-place update of a JSON column instead of removing the old document and writing the new document in its entirety to the column. This optimization can be performed for an update statement that uses the JSON_REPLACE() function and meets the conditions outlined in Partial Updates of JSON Values.

For a comparison of JSON_INSERT(), JSON_REPLACE(), and JSON_SET(), see the discussion of JSON_SET().

JSON_SET(json_doc, path, val[, path, val] ...)

Inserts or updates data in a JSON document and returns the result. Returns NULL if any argument is NULL or path, if given, does not locate an object. An error occurs if the json_doc argument is not a valid JSON document or any path argument is not a valid path expression or contains a * or ** wildcard.

The path-value pairs are evaluated left to right. The document produced by evaluating one pair becomes the new value against which the next pair is evaluated.

A path-value pair for an existing path in the document overwrites the existing document value with the new value. A path-value pair for a nonexisting path in the document adds the value to the document if the path identifies one of these types of values:

Otherwise, a path-value pair for a nonexisting path in the document is ignored and has no effect.

In MySQL 8.0.4, the optimizer can perform a partial, in-place update of a JSON column instead of removing the old document and writing the new document in its entirety to the column. This optimization can be performed for an update statement that uses the JSON_SET() function and meets the conditions outlined in Partial Updates of JSON Values.

The JSON_SET(), JSON_INSERT(), and JSON_REPLACE() functions are related:

The following examples illustrate these differences, using one path that does exist in the document ($.a) and another that does not exist ($.c):

JSON_UNQUOTE(json_val)

Unquotes JSON value and returns the result as a utf8mb4 string. Returns NULL if the argument is NULL. An error occurs if the value starts and ends with double quotes but is not a valid JSON string literal.

Within a string, certain sequences have special meaning unless the NO_BACKSLASH_ESCAPES SQL mode is enabled. Each of these sequences begins with a backslash (\), known as the escape character. MySQL recognizes the escape sequences shown in Table 12.22, “JSON_UNQUOTE() Special Character Escape Sequences”. For all other escape sequences, backslash is ignored. That is, the escaped character is interpreted as if it was not escaped. For example, \x is just x. These sequences are case-sensitive. For example, \b is interpreted as a backspace, but \B is interpreted as B.

Two simple examples of the use of this function are shown here:

The following set of examples shows how JSON_UNQUOTE handles escapes with NO_BACKSLASH_ESCAPES disabled and enabled: