Wordpress - How to change all the guid in posts table?

It should be something like:

UPDATE wp_posts SET guid = REPLACE(guid, 'oldurl.com', 'newurl.com') WHERE guid LIKE 'http://oldurl.com/%';

• oldurl.com - Previous URL shown in wordpress settings > general options
• newurl.com - New URL

To improve the previous answers you should update all relevant tables such as (here table prefix is wp_):

UPDATE `wp_posts` SET guid = REPLACE(guid, 'oldsiteurl', 'newsiteurl') WHERE guid LIKE 'oldsiteurl%';

UPDATE `wp_postmeta` SET meta_value = REPLACE(meta_value, 'oldsiteurl', 'newsiteurl') WHERE meta_value LIKE 'oldsiteurl%';

UPDATE `wp_options` SET option_value = REPLACE(option_value, 'oldsiteurl', 'newsiteurl') WHERE option_value LIKE 'oldsiteurl%';

If you got any plugins that do redirections you should also change the permalinks there:

UPDATE `wp_redirection_404` SET url = REPLACE(url, 'oldsiteurl', 'newsiteurl') WHERE url LIKE 'oldsiteurl%';