Primary Key

CREATE TABLE with PRIMARY CONSTRAINT

CREATE TABLE table_name (
	column1 datatype,
	column2 datatype,
	...
	columnN datatype,
	PRIMARY KEY(column1)
);

Adding PRIMARY KEY to an existing column

ALTER TABLE table_name ADD PRIMARY KEY(column_name);

You can also name your constraint while defining them. Using this method you can add it to multiple columns.

ALTER TABLE table_name ADD CONSTRAINT pk PRIMARY KEY(column_name);

DROPPING PRIMARY KEY

ALTER TABLE table_name DROP PRIMARY KEY;

You can drop named primary key using following syntax:

ALTER TABLE table_name DROP CONSTRAINT pk;