Primary keys - the basics
Single-column primary keys
Multicolumn primary keys
Auto-increment columns and sequences
Instruction
Okay, great. You should know that there are also some databases which do not have the AUTO_INCREMENT or IDENTITY columns. Instead, they use special objects called sequences. They are able to generate new numbers in a sequence, as the name suggests. Take a look:
CREATE SEQUENCE first_seq START WITH 1 INCREMENT BY 1;
You've probably guessed right what this code means. It will create a sequence named first_seq, with the initial value 1, increased by 1 each time.
Exercise
Let's do a quick exercise on creating sequences. Create a sequence with the name my_sequence which starts from 100 and increases the number by 10 each time.
Stuck? Here's a hint!
Type
CREATE SEQUENCE my_sequence START WITH 100 INCREMENT BY 10;
