JSON_OBJECTAGG
MariaDB starting with 10.5.0
JSON_OBJECTAGG was added in MariaDB 10.5.0.
Syntax
JSON_OBJECTAGG(key, value)
Description
JSON_OBJECTAGG returns a JSON object containing key-value pairs. It takes two expressions that evaluate to a single value, or two column names, as arguments, the first used as a key, and the second as a value.
The maximum returned length in bytes is determined by the group_concat_max_len server system variable.
Returns NULL in the case of an error, or if the result contains no rows.
JSON_OBJECTAGG cannot currently be used as a window function.
Examples
select * from t1;
+------+-------+
| a | b |
+------+-------+
| 1 | Hello |
| 1 | World |
| 2 | This |
+------+-------+
SELECT JSON_OBJECTAGG(a, b) FROM t1;
+----------------------------------------+
| JSON_OBJECTAGG(a, b) |
+----------------------------------------+
| {"1":"Hello", "1":"World", "2":"This"} |
+----------------------------------------+
Comments
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Repeated JSON Keys are valid and allowed in spec. It's just that most parsers of JSON will replace the previous key with the last one noted. In Javascript itself, you can parse as a array of [key, value] called "entries", but the default parser (JSON.parse) won't give you this.
How is this resulting JSON in the example what we would want? -- {"1":"Hello", "1":"World", "2":"This"} --
A more useful JSON result would be: -- {"1":["Hello","World"], "2":"This"} --
Or, if the function is expanded to take an additional third parameter JSON_OBJECTAGG(key, value,optional_keyfield_for_duplicate_values):
-- select * from t1; +------+-------+------+
+------+-------+------+
+------+-------+------+
SELECT JSON_OBJECTAGG(a, b, c) FROM t1; +---------------------------------------------+
+---------------------------------------------+
+---------------------------------------------+
--