MySQL Workbench - how to search all columns in every table
Open a new Query tab - from the File menu option choose the New Query item (second one down).

Then, it's exactly the same as in the MySQL tool.

use information_schema;
show tables;
SELECT * FROM columns;


will give the result:

Tables_in_information_schema
-----------------------------
CHARACTER_SETS
COLLATIONS
COLLATION_CHARACTER_SET_APPLICABILITY
COLUMNS                                &lt;&lt;--
COLUMN_PRIVILEGES
..
&lt;more columns snipped&gt;
..


For some reason, the information_schema database doesn't appear in the 
databases list in the GUI, but if you explicitly 'use' it, it will work.

Et voilà