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MySQL 8.0 Reference Manual  /  Data Types  /  The JSON Data Type

Pre-General Availability Draft: 2017-06-23

11.6 The JSON Data Type

MySQL supports a native JSON data type defined by RFC 7159 that enables efficient access to data in JSON (JavaScript Object Notation) documents. The JSON data type provides these advantages over storing JSON-format strings in a string column:

  • Automatic validation of JSON documents stored in JSON columns. Invalid documents produce an error.

  • Optimized storage format. JSON documents stored in JSON columns are converted to an internal format that permits quick read access to document elements. When the server later must read a JSON value stored in this binary format, the value need not be parsed from a text representation. The binary format is structured to enable the server to look up subobjects or nested values directly by key or array index without reading all values before or after them in the document.


This discussion uses JSON in monotype to indicate specifically the JSON data type and JSON in regular font to indicate JSON data in general.

The space required to store a JSON document is roughly the same as for LONGBLOB or LONGTEXT; see Section 11.8, “Data Type Storage Requirements”, for more information. It is important to keep in mind that the size of any JSON document stored in a JSON column is limited to the value of the max_allowed_packet system variable. (When the server is manipulating a JSON value internally in memory, it can be larger than this; the limit applies when the server stores it.) You can obtain the amount of space required to store a JSON document using the JSON_STORAGE_SIZE() function (introduced in MySQL 8.0.2); note that for a JSON column, the storage size—and thus the value returned by this function—is that used by the column prior to any partial updates that may have been performed on it (see the discussion of the JSON partial update optimization later in this section).

A JSON column cannot have a default value.

Along with the JSON data type, a set of SQL functions is available to enable operations on JSON values, such as creation, manipulation, and searching. The following discussion shows examples of these operations. For details about individual functions, see Section 12.16, “JSON Functions”.

A set of spatial functions for operating on GeoJSON values is also available. See Section 12.15.11, “Spatial GeoJSON Functions”.

JSON columns, like columns of other binary types, are not indexed directly; instead, you can create an index on a generated column that extracts a scalar value from the JSON column. See Indexing a Generated Column to Provide a JSON Column Index, for a detailed example.

The MySQL optimizer also looks for compatible indexes on virtual columns that match JSON expressions.

In MySQL 8.0 (8.0.2 and later), 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 that meets the following conditions:

  • The column being updated was declared as JSON.

  • The UPDATE statement uses any of the three functions JSON_SET(), JSON_REPLACE(), or JSON_REMOVE() to update the column. A direct assignment of the column value (for example, UPDATE mytable SET jcol = '{"a": 10, "b": 25'}) cannot be performed as a partial update.

    Updates of multiple JSON columns in a single UPDATE statement can be optimized in this fashion; MySQL can perform partial updates of only those columns whose values are updated using the three functions just listed.

  • The input column and the target column must be the same column; a statement such as UPDATE mytable SET jcol1 = JSON_SET(jcol2, '$.a', 100) cannot be performed as a partial update.

    The update can use nested calls to any of the functions listed in the previous item, in any combination, as long as the input and target columns are the same.

  • All changes replace existing array or object values with new ones, and do not add any new elements to the parent object or array.

  • The value being replaced must be at least as large as the replacement value. In other words, the new value cannot be any larger than the old one.

    A possible exception to this requirement jus stated can occur when a previous partial update has left sufficient space for the larger value. You can use the function JSON_STORAGE_FREE() see how much space was freed by the most recent partial update of a JSON column.

The next few sections provide basic information regarding the creation and manipulation of JSON values.

Creating JSON Values

A JSON array contains a list of values separated by commas and enclosed within [ and ] characters:

["abc", 10, null, true, false]

A JSON object contains a set of key-value pairs separated by commas and enclosed within { and } characters:

{"k1": "value", "k2": 10}

As the examples illustrate, JSON arrays and objects can contain scalar values that are strings or numbers, the JSON null literal, or the JSON boolean true or false literals. Keys in JSON objects must be strings. Temporal (date, time, or datetime) scalar values are also permitted:

["12:18:29.000000", "2015-07-29", "2015-07-29 12:18:29.000000"]

Nesting is permitted within JSON array elements and JSON object key values:

[99, {"id": "HK500", "cost": 75.99}, ["hot", "cold"]]
{"k1": "value", "k2": [10, 20]}

You can also obtain JSON values from a number of functions supplied by MySQL for this purpose (see Section 12.16.2, “Functions That Create JSON Values”) as well as by casting values of other types to the JSON type using CAST(value AS JSON) (see Converting between JSON and non-JSON values). The next several paragraphs describe how MySQL handles JSON values provided as input.

In MySQL, JSON values are written as strings. MySQL parses any string used in a context that requires a JSON value, and produces an error if it is not valid as JSON. These contexts include inserting a value into a column that has the JSON data type and passing an argument to a function that expects a JSON value (usually shown as json_doc or json_val in the documentation for MySQL JSON functions), as the following examples demonstrate:

  • Attempting to insert a value into a JSON column succeeds if the value is a valid JSON value, but fails if it is not:

    mysql> CREATE TABLE t1 (jdoc JSON);
    Query OK, 0 rows affected (0.20 sec)
    mysql> INSERT INTO t1 VALUES('{"key1": "value1", "key2": "value2"}');
    Query OK, 1 row affected (0.01 sec)
    mysql> INSERT INTO t1 VALUES('[1, 2,');
    ERROR 3140 (22032) at line 2: Invalid JSON text: 
    "Invalid value." at position 6 in value (or column) '[1, 2,'.

    Positions for at position N in such error messages are 0-based, but should be considered rough indications of where the problem in a value actually occurs.

  • The JSON_TYPE() function expects a JSON argument and attempts to parse it into a JSON value. It returns the value's JSON type if it is valid and produces an error otherwise:

    mysql> SELECT JSON_TYPE('["a", "b", 1]');
    | JSON_TYPE('["a", "b", 1]') |
    | ARRAY                      |
    mysql> SELECT JSON_TYPE('"hello"');
    | JSON_TYPE('"hello"') |
    | STRING               |
    mysql> SELECT JSON_TYPE('hello');
    ERROR 3146 (22032): Invalid data type for JSON data in argument 1
    to function json_type; a JSON string or JSON type is required.

MySQL handles strings used in JSON context using the utf8mb4 character set and utf8mb4_bin collation. Strings in other character sets are converted to utf8mb4 as necessary. (For strings in the ascii or utf8 character sets, no conversion is needed because ascii and utf8 are subsets of utf8mb4.)

As an alternative to writing JSON values using literal strings, functions exist for composing JSON values from component elements. JSON_ARRAY() takes a (possibly empty) list of values and returns a JSON array containing those values:

mysql> SELECT JSON_ARRAY('a', 1, NOW());
| JSON_ARRAY('a', 1, NOW())              |
| ["a", 1, "2015-07-27 09:43:47.000000"] |

JSON_OBJECT() takes a (possibly empty) list of key-value pairs and returns a JSON object containing those pairs:

mysql> SELECT JSON_OBJECT('key1', 1, 'key2', 'abc');
| JSON_OBJECT('key1', 1, 'key2', 'abc') |
| {"key1": 1, "key2": "abc"}            |

JSON_MERGE() takes two or more JSON documents and returns the combined result:

mysql> SELECT JSON_MERGE('["a", 1]', '{"key": "value"}');
| JSON_MERGE('["a", 1]', '{"key": "value"}') |
| ["a", 1, {"key": "value"}]                 |

For information about the merging rules, see Normalization, Merging, and Autowrapping of JSON Values.

JSON values can be assigned to user-defined variables:

mysql> SET @j = JSON_OBJECT('key', 'value');
mysql> SELECT @j;
| @j               |
| {"key": "value"} |

However, user-defined variables cannot be of JSON data type, so although @j in the preceding example looks like a JSON value and has the same character set and collation as a JSON value, it does not have the JSON data type. Instead, the result from JSON_OBJECT() is converted to a string when assigned to the variable.

Strings produced by converting JSON values have a character set of utf8mb4 and a collation of utf8mb4_bin:

| utf8mb4     | utf8mb4_bin   |

Because utf8mb4_bin is a binary collation, comparison of JSON values is case sensitive.

|                                 0 |

Case sensitivity also applies to the JSON null, true, and false literals, which always must be written in lowercase:

| JSON_VALID('null') | JSON_VALID('Null') | JSON_VALID('NULL') |
|                  1 |                  0 |                  0 |

mysql> SELECT CAST('null' AS JSON);
| CAST('null' AS JSON) |
| null                 |
1 row in set (0.00 sec)

ERROR 3141 (22032): Invalid JSON text in argument 1 to function cast_as_json:
"Invalid value." at position 0 in 'NULL'.

Case sensitivity of the JSON literals differs from that of the SQL NULL, TRUE, and FALSE literals, which can be written in any lettercase:

| ISNULL(null) | ISNULL(Null) | ISNULL(NULL) |
|            1 |            1 |            1 |

Sometimes it may be necessary or desirable to insert quote characters (" or ') into a JSON document. Assume for this example that you want to insert some JSON objects containing strings representing sentences that state some facts about MySQL, each paired with an appropriate keyword, into a table created using the SQL statement shown here:

mysql> CREATE TABLE facts (sentence JSON);

Among these keyword-sentence pairs is this one:

mascot: The MySQL mascot is a dolphin named "Sakila".

One way to insert this as a JSON object into the facts table is to use the MySQL JSON_OBJECT() function. In this case, you must escape each quote character using a backslash, as shown here:

mysql> INSERT INTO facts VALUES 
     >   (JSON_OBJECT("mascot", "Our mascot is a dolphin named \"Sakila\"."));

This does not work in the same way if you insert the value as a JSON object literal, in which case, you must use the double backslash escape sequence, like this:

mysql> INSERT INTO facts VALUES 
     >   ('{"mascot": "Our mascot is a dolphin named \\"Sakila\\"."}');

Using the double backslash keeps MySQL from performing escape sequence processing, and instead causes it to pass the string literal to the storage engine for processing. After inserting the JSON object in either of the ways just shown, you can see that the backslashes are present in the JSON column value by doing a simple SELECT, like this:

mysql> SELECT sentence FROM facts;
| sentence                                                |
| {"mascot": "Our mascot is a dolphin named \"Sakila\"."} |

To look up this particular sentence employing mascot as the key, you can use the column-path operator ->, as shown here:

mysql> SELECT col->"$.mascot" FROM qtest;
| col->"$.mascot"                             |
| "Our mascot is a dolphin named \"Sakila\"." |
1 row in set (0.00 sec)

This leaves the backslashes intact, along with the surrounding quote marks. To display the desired value using mascot as the key, but without including the surrounding quote marks or any escapes, use the inline path operator ->>, like this:

mysql> SELECT sentence->>"$.mascot" FROM facts;
| sentence->>"$.mascot"                   |
| Our mascot is a dolphin named "Sakila". |

The previous example does not work as shown if the NO_BACKSLASH_ESCAPES server SQL mode is enabled. If this mode is set, a single backslash instead of double backslashes can be used to insert the JSON object literal, and the backslashes are preserved. If you use the JSON_OBJECT() function when performing the insert and this mode is set, you must alternate single and double quotes, like this:

mysql> INSERT INTO facts VALUES 
     > (JSON_OBJECT('mascot', 'Our mascot is a dolphin named "Sakila".'));

See the description of the JSON_UNQUOTE() function for more information about the effects of this mode on escaped characters in JSON values.

Normalization, Merging, and Autowrapping of JSON Values

When a string is parsed and found to be a valid JSON document, it is also normalized: Members with keys that duplicate a key found earlier in the document are discarded (even if the values differ). The object value produced by the following JSON_OBJECT() call does not include the second key1 element because that key name occurs earlier in the value:

mysql> SELECT JSON_OBJECT('key1', 1, 'key2', 'abc', 'key1', 'def');
| JSON_OBJECT('key1', 1, 'key2', 'abc', 'key1', 'def') |
| {"key1": 1, "key2": "abc"}                           |

The normalization performed by MySQL also sorts the keys of a JSON object (for the purpose of making lookups more efficient). The result of this ordering is subject to change and not guaranteed to be consistent across releases. In addition, extra whitespace between keys, values, or elements in the original document is discarded.

MySQL functions that produce JSON values (see Section 12.16.2, “Functions That Create JSON Values”) always return normalized values.

In contexts that combine multiple arrays, the arrays are merged into a single array by concatenating arrays named later to the end of the first array. In the following example, JSON_MERGE() merges its arguments into a single array:

mysql> SELECT JSON_MERGE('[1, 2]', '["a", "b"]', '[true, false]');
| JSON_MERGE('[1, 2]', '["a", "b"]', '[true, false]') |
| [1, 2, "a", "b", true, false]                       |

Multiple objects when merged produce a single object. If multiple objects have the same key, the value for that key in the resulting merged object is an array containing the key values:

mysql> SELECT JSON_MERGE('{"a": 1, "b": 2}', '{"c": 3, "a": 4}');
| JSON_MERGE('{"a": 1, "b": 2}', '{"c": 3, "a": 4}') |
| {"a": [1, 4], "b": 2, "c": 3}                      |

Nonarray values used in a context that requires an array value are autowrapped: The value is surrounded by [ and ] characters to convert it to an array. In the following statement, each argument is autowrapped as an array ([1], [2]). These are then merged to produce a single result array:

mysql> SELECT JSON_MERGE('1', '2');
| JSON_MERGE('1', '2') |
| [1, 2]               |

Array and object values are merged by autowrapping the object as an array and merging the two arrays:

mysql> SELECT JSON_MERGE('[10, 20]', '{"a": "x", "b": "y"}');
| JSON_MERGE('[10, 20]', '{"a": "x", "b": "y"}') |
| [10, 20, {"a": "x", "b": "y"}]                 |

Searching and Modifying JSON Values

A JSON path expression selects a value within a JSON document.

Path expressions are useful with functions that extract parts of or modify a JSON document, to specify where within that document to operate. For example, the following query extracts from a JSON document the value of the member with the name key:

mysql> SELECT JSON_EXTRACT('{"id": 14, "name": "Aztalan"}', '$.name');
| JSON_EXTRACT('{"id": 14, "name": "Aztalan"}', '$.name') |
| "Aztalan"                                               |

Path syntax uses a leading $ character to represent the JSON document under consideration, optionally followed by selectors that indicate successively more specific parts of the document:

  • A period followed by a key name names the member in an object with the given key. The key name must be specified within double quotation marks if the name without quotes is not legal within path expressions (for example, if it contains a space).

  • [N] appended to a path that selects an array names the value at position N within the array. Array positions are integers beginning with zero.

  • (MySQL 8.0.2 and later:) [M to N] specifies a subset or range of array values starting with the value at position M, and ending with the value at position N.

    last is supported as a synonym for the index of the rightmost array element. Relative addressing of array elements is also supported.

  • Paths can contain * or ** wildcards:

    • .[*] evaluates to the values of all members in a JSON object.

    • [*] evaluates to the values of all elements in a JSON array.

    • prefix**suffix evaluates to all paths that begin with the named prefix and end with the named suffix.

  • A path that does not exist in the document (evaluates to nonexistent data) evaluates to NULL.

Let $ refer to this JSON array with three elements:

[3, {"a": [5, 6], "b": 10}, [99, 100]]


  • $[0] evaluates to 3.

  • $[1] evaluates to {"a": [5, 6], "b": 10}.

  • $[2] evaluates to [99, 100].

  • $[3] evaluates to NULL (it refers to the fourth array element, which does not exist).

Because $[1] and $[2] evaluate to nonscalar values, they can be used as the basis for more-specific path expressions that select nested values. Examples:

  • $[1].a evaluates to [5, 6].

  • $[1].a[1] evaluates to 6.

  • $[1].b evaluates to 10.

  • $[2][0] evaluates to 99.

As mentioned previously, path components that name keys must be quoted if the unquoted key name is not legal in path expressions. Let $ refer to this value:

{"a fish": "shark", "a bird": "sparrow"}

The keys both contain a space and must be quoted:

  • $."a fish" evaluates to shark.

  • $."a bird" evaluates to sparrow.

Paths that use wildcards evaluate to an array that can contain multiple values:

mysql> SELECT JSON_EXTRACT('{"a": 1, "b": 2, "c": [3, 4, 5]}', '$.*');
| JSON_EXTRACT('{"a": 1, "b": 2, "c": [3, 4, 5]}', '$.*') |
| [1, 2, [3, 4, 5]]                                       |
mysql> SELECT JSON_EXTRACT('{"a": 1, "b": 2, "c": [3, 4, 5]}', '$.c[*]');
| JSON_EXTRACT('{"a": 1, "b": 2, "c": [3, 4, 5]}', '$.c[*]') |
| [3, 4, 5]                                                  |

In the following example, the path $**.b evaluates to multiple paths ($.a.b and $.c.b) and produces an array of the matching path values:

mysql> SELECT JSON_EXTRACT('{"a": {"b": 1}, "c": {"b": 2}}', '$**.b');
| JSON_EXTRACT('{"a": {"b": 1}, "c": {"b": 2}}', '$**.b') |
| [1, 2]                                                  |

Beginning with MySQL 8.0.2, you can use ranges with the to keyword to specify subsets of JSON arrays. For example, $[1 to 3] includes the second, third, and fourth elements of an array, as shown here:

mysql> SELECT JSON_EXTRACT('[1, 2, 3, 4, 5]', '$[1 to 3]');
| JSON_EXTRACT('[1, 2, 3, 4, 5]', '$[1 to 3]') |
| [2, 3, 4]                                    |
1 row in set (0.00 sec)

The syntax is M to N, where M and N are, respectively, the first and last indexes of a range of elements from a JSON array. N must be greater than M; M must be greater than or equal to 0. Array elements are indexed beginning with 0.

You can use ranges in contexts where wildcards are supported.

Beginning with MySQL 8.0.2, the last keyword is supported as a synonym for the index of the last element in an array. Expressions of the form last - N can be used for relative addressing, and within range definitions, like this:

mysql> SELECT JSON_EXTRACT('[1, 2, 3, 4, 5]', '$[last-3 to last-1]');
| JSON_EXTRACT('[1, 2, 3, 4, 5]', '$[last-3 to last-1]') |
| [2, 3, 4]                                              |
1 row in set (0.01 sec)

If the path is evaluated against a value that is not an array, the result of the evaluation is the same as if the value had been wrapped in a single-element array:

mysql> SELECT JSON_REPLACE('"Sakila"', '$[last]', 10);
| JSON_REPLACE('"Sakila"', '$[last]', 10) |
| 10                                      |
1 row in set (0.00 sec)

You can use column->path with a JSON column identifier and JSON path expression as a synonym for JSON_EXTRACT(column, path). See Section 12.16.3, “Functions That Search JSON Values”, for more information. See also Indexing a Generated Column to Provide a JSON Column Index.

Some functions take an existing JSON document, modify it in some way, and return the resulting modified document. Path expressions indicate where in the document to make changes. For example, the JSON_SET(), JSON_INSERT(), and JSON_REPLACE() functions each take a JSON document, plus one or more path-value pairs that describe where to modify the document and the values to use. The functions differ in how they handle existing and nonexisting values within the document.

Consider this document:

mysql> SET @j = '["a", {"b": [true, false]}, [10, 20]]';

JSON_SET() replaces values for paths that exist and adds values for paths that do not exist:.

mysql> SELECT JSON_SET(@j, '$[1].b[0]', 1, '$[2][2]', 2);
| JSON_SET(@j, '$[1].b[0]', 1, '$[2][2]', 2) |
| ["a", {"b": [1, false]}, [10, 20, 2]]      |

In this case, the path $[1].b[0] selects an existing value (true), which is replaced with the value following the path argument (1). The path $[2][2] does not exist, so the corresponding value (2) is added to the value selected by $[2].

JSON_INSERT() adds new values but does not replace existing values:

mysql> SELECT JSON_INSERT(@j, '$[1].b[0]', 1, '$[2][2]', 2);
| JSON_INSERT(@j, '$[1].b[0]', 1, '$[2][2]', 2) |
| ["a", {"b": [true, false]}, [10, 20, 2]]      |

JSON_REPLACE() replaces existing values and ignores new values:

mysql> SELECT JSON_REPLACE(@j, '$[1].b[0]', 1, '$[2][2]', 2);
| JSON_REPLACE(@j, '$[1].b[0]', 1, '$[2][2]', 2) |
| ["a", {"b": [1, false]}, [10, 20]]             |

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.

JSON_REMOVE() takes a JSON document and one or more paths that specify values to be removed from the document. The return value is the original document minus the values selected by paths that exist within the document:

mysql> SELECT JSON_REMOVE(@j, '$[2]', '$[1].b[1]', '$[1].b[1]');
| JSON_REMOVE(@j, '$[2]', '$[1].b[1]', '$[1].b[1]') |
| ["a", {"b": [true]}]                              |

The paths have these effects:

  • $[2] matches [10, 20] and removes it.

  • The first instance of $[1].b[1] matches false in the b element and removes it.

  • The second instance of $[1].b[1] matches nothing: That element has already been removed, the path no longer exists, and has no effect.

Comparison and Ordering of JSON Values

JSON values can be compared using the =, <, <=, >, >=, <>, !=, and <=> operators.

The following comparison operators and functions are not yet supported with JSON values:

A workaround for the comparison operators and functions just listed is to cast JSON values to a native MySQL numeric or string data type so they have a consistent non-JSON scalar type.

Comparison of JSON values takes place at two levels. The first level of comparison is based on the JSON types of the compared values. If the types differ, the comparison result is determined solely by which type has higher precedence. If the two values have the same JSON type, a second level of comparison occurs using type-specific rules.

The following list shows the precedences of JSON types, from highest precedence to the lowest. (The type names are those returned by the JSON_TYPE() function.) Types shown together on a line have the same precedence. Any value having a JSON type listed earlier in the list compares greater than any value having a JSON type listed later in the list.


For JSON values of the same precedence, the comparison rules are type specific:

  • BLOB

    The first N bytes of the two values are compared, where N is the number of bytes in the shorter value. If the first N bytes of the two values are identical, the shorter value is ordered before the longer value.

  • BIT

    Same rules as for BLOB.


    Same rules as for BLOB. OPAQUE values are values that are not classified as one of the other types.


    A value that represents an earlier point in time is ordered before a value that represents a later point in time. If two values originally come from the MySQL DATETIME and TIMESTAMP types, respectively, they are equal if they represent the same point in time.

  • TIME

    The smaller of two time values is ordered before the larger one.

  • DATE

    The earlier date is ordered before the more recent date.


    Two JSON arrays are equal if they have the same length and values in corresponding positions in the arrays are equal.

    If the arrays are not equal, their order is determined by the elements in the first position where there is a difference. The array with the smaller value in that position is ordered first. If all values of the shorter array are equal to the corresponding values in the longer array, the shorter array is ordered first.


    [] < ["a"] < ["ab"] < ["ab", "cd", "ef"] < ["ab", "ef"]

    The JSON false literal is less than the JSON true literal.


    Two JSON objects are equal if they have the same set of keys, and each key has the same value in both objects.


    {"a": 1, "b": 2} = {"b": 2, "a": 1}

    The order of two objects that are not equal is unspecified but deterministic.


    Strings are ordered lexically on the first N bytes of the utf8mb4 representation of the two strings being compared, where N is the length of the shorter string. If the first N bytes of the two strings are identical, the shorter string is considered smaller than the longer string.


    "a" < "ab" < "b" < "bc"

    This ordering is equivalent to the ordering of SQL strings with collation utf8mb4_bin. Because utf8mb4_bin is a binary collation, comparison of JSON values is case sensitive:

    "A" < "a"

    JSON values can contain exact-value numbers and approximate-value numbers. For a general discussion of these types of numbers, see Section 9.1.2, “Number Literals”.

    The rules for comparing native MySQL numeric types are discussed in Section 12.2, “Type Conversion in Expression Evaluation”, but the rules for comparing numbers within JSON values differ somewhat:

    • In a comparison between two columns that use the native MySQL INT and DOUBLE numeric types, respectively, it is known that all comparisons involve an integer and a double, so the integer is converted to double for all rows. That is, exact-value numbers are converted to approximate-value numbers.

    • On the other hand, if the query compares two JSON columns containing numbers, it cannot be known in advance whether numbers will be integer or double. To provide the most consistent behavior across all rows, MySQL converts approximate-value numbers to exact-value numbers. The resulting ordering is consistent and does not lose precision for the exact-value numbers. For example, given the scalars 9223372036854775805, 9223372036854775806, 9223372036854775807 and 9.223372036854776e18, the order is such as this:

      9223372036854775805 < 9223372036854775806 < 9223372036854775807
      < 9.223372036854776e18 = 9223372036854776000 < 9223372036854776001

    Were JSON comparisons to use the non-JSON numeric comparison rules, inconsistent ordering could occur. The usual MySQL comparison rules for numbers yield these orderings:

    • Integer comparison:

      9223372036854775805 < 9223372036854775806 < 9223372036854775807

      (not defined for 9.223372036854776e18)

    • Double comparison:

      9223372036854775805 = 9223372036854775806 = 9223372036854775807 = 9.223372036854776e18

For comparison of any JSON value to SQL NULL, the result is UNKNOWN.

For comparison of JSON and non-JSON values, the non-JSON value is converted to JSON according to the rules in the following table, then the values compared as described previously.

Converting between JSON and non-JSON values

The following table provides a summary of the rules that MySQL follows when casting between JSON values and values of other types:

Table 11.2 JSON Conversion Rules

other type CAST(other type AS JSON) CAST(JSON AS other type)
JSON No change No change
utf8 character type (utf8mb4, utf8, ascii) The string is parsed into a JSON value. The JSON value is serialized into a utf8mb4 string.
Other character types Other character encodings are implicitly converted to utf8mb4 and treated as described for utf8 character type. The JSON value is serialized into a utf8mb4 string, then cast to the other character encoding. The result may not be meaningful.
NULL Results in a NULL value of type JSON. Not applicable.
Geometry types The geometry value is converted into a JSON document by calling ST_AsGeoJSON(). Illegal operation. Workaround: Pass the result of CAST(json_val AS CHAR) to ST_GeomFromGeoJSON().
All other types Results in a JSON document consisting of a single scalar value. Succeeds if the JSON document consists of a single scalar value of the target type and that scalar value can be cast to the target type. Otherwise, returns NULL and produces a warning.

ORDER BY and GROUP BY for JSON values works according to these principles:

  • Ordering of scalar JSON values uses the same rules as in the preceding discussion.

  • For ascending sorts, SQL NULL orders before all JSON values, including the JSON null literal; for descending sorts, SQL NULL orders after all JSON values, including the JSON null literal.

  • Sort keys for JSON values are bound by the value of the max_sort_length system variable, so keys that differ only after the first max_sort_length bytes compare as equal.

  • Sorting of nonscalar values is not currently supported and a warning occurs.

For sorting, it can be beneficial to cast a JSON scalar to some other native MySQL type. For example, if a column named jdoc contains JSON objects having a member consisting of an id key and a nonnegative value, use this expression to sort by id values:


If there happens to be a generated column defined to use the same expression as in the ORDER BY, the MySQL optimizer recognizes that and considers using the index for the query execution plan. See Section 8.3.10, “Optimizer Use of Generated Column Indexes”.

Aggregation of JSON Values

For aggregation of JSON values, SQL NULL values are ignored as for other data types. Non-NULL values are converted to a numeric type and aggregated, except for MIN(), MAX(), and GROUP_CONCAT(). The conversion to number should produce a meaningful result for JSON values that are numeric scalars, although (depending on the values) truncation and loss of precision may occur. Conversion to number of other JSON values may not produce a meaningful result.

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