Extract data from JSON string inside a MySQL field. In this case, extract metadesc and page title from the menu params

extract-string.sql

SELECT m.id, m.title,
    @tmp_search := '"menu-meta_description":"' AS tmp_search,
    @tmp_search_len := LENGTH(@tmp_search) AS tmp_search_len,
    @start := LOCATE(@tmp_search, m.params) AS tmp_start,
    @end := LOCATE('"', m.params, @start + @tmp_search_len) AS tmp_end,
    SUBSTRING(m.params, @start + @tmp_search_len, @end - @start - @tmp_search_len) AS metadesc,
    
    @tmp_search := '"page_title":"' AS tmp_search,
    @tmp_search_len := LENGTH(@tmp_search) AS tmp_search_len,
    @start := LOCATE(@tmp_search, m.params) AS tmp_start,
    @end := LOCATE('"', m.params, @start + @tmp_search_len) AS tmp_end,
    SUBSTRING(m.params, @start + @tmp_search_len, @end - @start - @tmp_search_len) AS metatitle
FROM j_menu AS m