Fix for corrupt JSON strings in Joomla database

update.sql

-- Phil Taylor <phil@phil-taylor.com>
-- @see https://github.com/joomla/joomla-cms/issues/12460
-- replace jos_ with your database prefix (left as jos and not #__ for syntax highlighting)
-- This is not a COMPLETE fix, this only fixes SOME of the core columns in tables that contain JSON.
-- BACKUP YOUR DATABASE BEFORE RUNNING THIS!!!!!!

UPDATE jos_modules SET params = "{}" WHERE params = "" OR params = '{\"\"}' OR params = '{\\\"\\\"}';
UPDATE jos_menu SET params = "{}" WHERE params = "" OR params = '{\"\"}' OR params = '{\\\"\\\"}';
UPDATE jos_extensions SET params = "{}" WHERE params = "" OR params = '{\"\"}' OR params = '{\\\"\\\"}';
UPDATE jos_assets SET rules = "{}" WHERE rules = "" OR rules = '{\"\"}' OR rules = '{\\\"\\\"}';

-- Run the above SQL FIRST and see if that fixes your site - if not continue and run these additional sql queries, you may not need these!
-- DO NOT run this if you are using Widgetkit because they stupidly have json, within json... 

UPDATE jos_modules SET params = REPLACE(params, '\\"', '"');
UPDATE jos_menu SET params = REPLACE(params, '\\"', '"');
UPDATE jos_extensions SET params = REPLACE(params, '\\"', '"');
UPDATE jos_assets SET rules = REPLACE(rules, '\\"', '"');