Hello everybody

Suppose I have two related tables. The relation is only one to one. That means that only a single record of the first table can be referenced via a foreign key in the second. Can I express such a thing using database constraints or do I have to make my checks in code?

thx, in advance

George Papadopoulos

your comment "only a single record of the first table can be referenced via a foreign key in the second" is true for one-to-many tables as well

in a one-to-one relationship, at most one record of the second table can have a foreign key referencing any single record in the first table

for mysql, use innodb tables in order to get foreign key support

to restrict the relationship to one-to-one, you would use a CHECK constraint, and i don't think mysql supports it