How can I ensure that there is one-and-only-one row in DB table?

I would like to ensure that my MySQL table myTable has one-and-only-one row.

I need to be able to Update this row but Insert and Remove should be not possible.

I am asking this question because of this answer to How to create a "unique" constraint on a boolean MySQL column?.

Two suggestions for you, one or both which may work depending on the particulars of the data you're trying to store:

• See if the ENUM or SET constraints will work for you; note that they offer differing levels of enforcement based on SQL mode (e.g., strict). See more info:

  http://dev.mysql.com/doc/refman/5.0/en/constraint-invalid-data.html

AND/OR

• Implement INSERT, UPDATE, and DELETE triggers to control access on the data (you may want to populate the data initially before you create these; again, it depends on your scenario)

  http://dev.mysql.com/doc/refman/5.0/en/create-trigger.html