I would like to ensure that my MySQL table named "myTable" has one-and-only-one row.
So I need to be able to do Update on this row but obviously Insert and Remove should be not possible.
I am asking this question because of this Stack Overflow answer
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:
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)