无法在mysql表上创建外键

Question

When I try this

ALTER TABLE Comp_Entry
ADD FOREIGN KEY(CompetitionID) REFERENCES Comp__Competition(CompetitionID)

I get this error

#1005 - Can't create table 'chris_db.#sql-1464b_66' (errno: 150) (<a href="server_engines.php?engine=InnoDB&amp;page=Status&amp;token=7a7f690fbd1413e74979d79fa9044fb0">Details...</a>)

My Comp_Competition table has CompetitionID set as the primary key. Is anyone familiar with this problem?

Answer 1

Your Comp_Entry table needs an existing index for CompetitionID. Also, your command has a double __ characters in the name for table Comp__Competition, but in your explanation you have only one. Which one is right?

Answer 2

Because there is data in your table which does not feet to your constraint (for example nonexistent keys)

try to make

     select * from Comp_Entry where CompetitionID not in 
        (select distinct CompetitionID from Comp__Competition)