Question

I define table 1.
Now i want to add new table – and one of the column of the second table need to be the first table –

How can i do it ?

Answer 1

If you want one column of a table to reference another table, then your best bet is probably to go read up on the concept of keys, primary keys, and foreign keys in database design.

For example, in a database of companies and employees, you might have 2 tables like this:

Company (c_id, name, city)
Employee (e_id, c_id, name)

In the Company table, c_id would be a primary key. In the Employee table, c_id would be a foreign key referencing Company. This would allow you to do queries like

SELECT E.name
FROM Employee as E, Company as C
WHERE E.c_id = C.c_id AND C.name = "IBM"

which would return the names of employees who work at IBM.

Links:

http://en.wikipedia.org/wiki/Primary_key

http://en.wikipedia.org/wiki/Foreign_key