1A primary key allows each record in a table to be uniquely identified. There can only be one
2primary key per table, and you can assign this constraint to any single or combination of columns.
3However, this means each value within this column(s) must be unique.
4Typically in a table, the primary key is an ID column, and is usually paired with the AUTO_
5INCREMENT keyword. This means the value increases automatically as new records are created.
6CREATE TABLE users (
7id int NOT NULL AUTO_INCREMENT,
8first_name varchar(255),
9last_name varchar(255) NOT NULL,
10address varchar(255),
11email varchar(255),
12PRIMARY KEY (id)
13);
1/* A primary key allows each record in a table to be uniquely identified. There can only be one
2primary key per table, and you can assign this constraint to any single or combination of columns.
3However, this means each value within this column(s) must be unique.
4Typically in a table, the primary key is an ID column, and is usually paired with the AUTO_
5INCREMENT keyword. This means the value increases automatically as new records are created. */
6CREATE TABLE stats(id INT NOT NULL PRIMARY KEY, name TEXT)
1-- NOTE: this is for SQL-Oracle specifically
2
3-- syntax:
4SELECT cols.table_name, cols.column_name, cols.position, cons.status, cons.owner
5FROM all_constraints cons, all_cons_columns cols
6WHERE cols.table_name = '<table-name>' -- Replace <table-name> with your table-name
7AND cons.constraint_type = 'P'
8AND cons.constraint_name = cols.constraint_name
9AND cons.owner = cols.owner
10
11
12-- example:
13SELECT cols.table_name, cols.column_name, cols.position, cons.status, cons.owner
14FROM all_constraints cons, all_cons_columns cols
15WHERE cols.table_name = 'CUSTOMERS'
16AND cons.constraint_type = 'P'
17AND cons.constraint_name = cols.constraint_name
18AND cons.owner = cols.owner
1PRIMARY KEY
2 -- unique identifier for the entire row of record in a table
3 -- can not be null and must be unique
1The PRIMARY KEY constraint uniquely identifies each record in a table.
2Primary keys must contain UNIQUE values, and cannot contain NULL values.
3A table can have only ONE primary key; and in the table, this primary key can consist of single or multiple columns (fields).
4
1Primary Key :
2It is unique column in every table in a database
3It can ONLY accept;
4 - nonduplicate values
5 - cannot be NULL