This reply might be a little too late but here's what I think... You're probably getting that error because you typed in the wrong syntax. To show tables from any mysql database, you should first tell the mysql command line what table to use... you can do this by typing:
USE table_name;
Where "table_name" represent the name of the table you want to use.
Only after that can you tell mysql to show the contents of the selected table. That's why when you typed this code:
SHOW TABLES;
mysql worked properly. That's probably because the database that you are using is currently selected by default or is the only database available in your site.