[GENERAL] foreign key to "some rows" of a second table

[Chris Withers]

Hi All, So, I have a table that looks like this: CREATE TABLE config (     region    varchar(10),     name    varchar(10),     value    varchar(40) ); Another looks like this: CREATE TABLE tag (     host    varchar(10),     type    varchar(10),     value    varchar(10) ); What's the best way to set up a constraint on the 'config' table such that the 'region' column can only contain values that exist in the 'tag' table's value column where the 'type' is 'region'? cheers, Chris