primary key example in sql

Example 1: sql primary key

A primary key allows each record in a table to be uniquely identified. There can only be one
primary key per table, and you can assign this constraint to any single or combination of columns.
However, this means each value within this column(s) must be unique.
Typically in a table, the primary key is an ID column, and is usually paired with the AUTO_
INCREMENT keyword. This means the value increases automatically as new records are created.
CREATE TABLE users (
id int NOT NULL AUTO_INCREMENT,
first_name varchar(255),
last_name varchar(255) NOT NULL,
address varchar(255),
email varchar(255),
PRIMARY KEY (id)
);

Example 2: sql primary key

-- NOTE: this is for SQL-Oracle specifically

-- example:
SELECT cols.table_name, cols.column_name, cols.position, cons.status, cons.owner
FROM all_constraints cons, all_cons_columns cols
WHERE cols.table_name = 'CUSTOMERS' 
AND cons.constraint_type = 'P'
AND cons.constraint_name = cols.constraint_name
AND cons.owner = cols.owner;

-- syntax:
SELECT cols.table_name, cols.column_name, cols.position, cons.status, cons.owner
FROM all_constraints cons, all_cons_columns cols
WHERE cols.table_name = '<table-name>' -- Replace <table-name> with your table-name
AND cons.constraint_type = 'P'
AND cons.constraint_name = cols.constraint_name
AND cons.owner = cols.owner;

Example 3: primary key sql

CREATE TABLE student

(

Roll integer (15) NOT NULL PRIMARY KEY,

Name varchar (255),

Class varchar (255),

Contact No varchar (255),

);

Example 4: primary key in sql

The PRIMARY KEY constraint uniquely identifies each record in a table.
Primary keys must contain UNIQUE values, and cannot contain NULL values. 
A table can have only ONE primary key; and in the table, this primary key can consist of single or multiple columns (fields).