selecting all field_data_body for all content types
I needed to do something a bit similar a while ago, and used the drupal field definition tables to identify the field type (text/long et al) and work from there to the nodes. I suggest you do likewise.

You could consider using the mysql fulltext search facilities - it is much faster and much more capable than 'like'.

Of course, the drupal way would be to configure the search module properly...