I dont quite understand the user of primary key

[ilyalyu]

What primary keys are used for? I know that if I want to create index, I can use index keyword. I have keywords for creating unique and autoincrementing columns. It seems that I can do everithing what I need with other keywords. So can anybody explain why I need to use primary keys and in what situations?

[r937]

for relating another table to this table with a foreign key

[ilyalyu]

But I can join two tables without primary key using 'where' statement. I can use ANY column.

[r937]

yes, you can join on whatever you want

primary and foreign keys are used to ensure relational integrity

this is often a new concept to mysql programmers, because mysql doesn't support relational integrity unless you use innodb tables