I would like to set up a DB table which should contain the id's of another table. This info (id) are placed in just one table cell. What shall I do?
To be more specific: there's a table called "developers". There should be info like email, name, his skills, and the id's in which this developer has participated. The project's table of course is already existing.
So when the visitor loads this developer's page, he should get a list of projects which this corresponding developer has joined.
Indeed, as soon as you find yourself trying to store multiple values in a single database table, you should re-think your database design. The relationship of developers to projects is a many-to-many relationship. Read the chapter on Relational Database Design in my article to find out how to set up a lookup table to model this relationship.