sqlmysqlmysql-json

SQL query to update JSON field value in MySQL


Using MySQL, I need to update record where there is a null value in a field of type json. For example,

Table 1

Column A Column B
Cell 1 [{"id":1, "name":"abc"},{"id":2, "name":"xyz"},{"id":3, "name":null}]
Cell 2 [{"id":4, "name":"test 1"},{"id":5, "name":null}]

Table 2

id name
1 abc
2 xyz
3 null
4 test 1
5 null

I wrote this query to first retrieve the records where null value is stored in name key

SELECT *
FROM table 1
WHERE JSON_CONTAINS(column B, '{"name": null}', '$');

Now I need to update the records using an SQL query to delete the object from the array in table 1 column B. Table 1 should like this.

Table 1

Column A Column B
Cell 1 [{"id":1, "name":"abc"},{"id":2, "name":"xyz"}]
Cell 2 [{"id":4, "name":"test 1"}]

How can I achieve this without writing stored procedures?

I tried updating one record using this query

UPDATE table 1
SET column_B = JSON_ARRAY(
    JSON_OBJECT(
       "id", JSON_UNQUOTE(JSON_EXTRACT(column_B, '$[0].id')), 
       "name", JSON_UNQUOTE(JSON_EXTRACT(injuries, '$[0].name'))
    ),
)
WHERE id = 1;

Solution

  • There is a JSON function JSON_TABLE, which used to convert each JSON array into number of JSON Objects(rows) contains in that JSON Array. Let if a JSON array contact n JSON object, then it'll create n rows for Each Object which exists in that JSON array.

    For Example:
    Lets, my Input is:
    enter image description here

    I want to break as follows:
    enter image description here

    set @jsonArray = JSON_ARRAY(
         JSON_OBJECT('key', 1, 'value', 'Data1'), 
         JSON_OBJECT('key', 2, 'value', 'Data2'), 
         JSON_OBJECT('key', 3, 'value', 'Data3')
    );
    
    select * 
    from JSON_TABLE(
        @jsArray, '$[*]' COLUMNS (
            split_json_array JSON PATH '$'
        )
    ) AS JT
    

    Similar way we need to convert all 'Column B' JSON array value into respective format. Then we have to apply condition, split_json_array->>'$.name' = 'null' filter 'Column B' JSON Array elements, which name is exits, and then need to merge those data.

    So, respective query is:

    WITH Base_Table_1 AS (
        select * from 
            Table_1,
            JSON_TABLE(column_B, '$[*]' COLUMNS (
                split_json_array JSON PATH '$'
            )) AS jt
    ),
    filter_Table_1 AS (
        SELECT
            column_A,
            JSON_ARRAYAGG(split_json_array) AS column_B_filtered_data
        from Base_Table_1
        where split_json_array->>'$.name' != 'null'
        group by column_A
    )
    Select * from filter_Table_1;
    

    Output:
    enter image description here

    Next update your Table_1 table column_B value from filter_Table_1 table:

    UPDATE Table_1
    SET column_B = (
        select filter_Table_1.column_B_filtered_data
        From filter_Table_1
        WHERE Table_1.column_A = filter_Table_1.column_A
    );
    

    So, latest Table_1 is showing as:

    select * from Table_1;
    

    enter image description here

    Sample code for live testing: myCompiler

    Needs lots of research & investigation for this and I learn something new related to MySQL JSON Data handling.

    I hope your issue will resolve.
    Thank you for this question.