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)
1A primary key is a field in a table which uniquely identifies each row/record in a database table. Primary keys must contain unique values. A primary key column cannot have NULL values.
2
3A table can have only one primary key, which may consist of single or multiple fields. When multiple fields are used as a primary key, they are called a composite key.
4
5If a table has a primary key defined on any field(s), then you cannot have two records having the same value of that field(s).
1-- NOTE: this is for SQL-Oracle specifically
2
3-- example:
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 = 'CUSTOMERS'
7AND cons.constraint_type = 'P'
8AND cons.constraint_name = cols.constraint_name
9AND cons.owner = cols.owner;
10
11-- syntax:
12SELECT cols.table_name, cols.column_name, cols.position, cons.status, cons.owner
13FROM all_constraints cons, all_cons_columns cols
14WHERE cols.table_name = '<table-name>' -- Replace <table-name> with your table-name
15AND cons.constraint_type = 'P'
16AND cons.constraint_name = cols.constraint_name
17AND cons.owner = cols.owner;
18
1PRIMARY KEY
2 -- unique identifier for the entire row of record in a table
3 -- can not be null and must be unique
1CREATE TABLE student
2
3(
4
5Roll integer (15) NOT NULL PRIMARY KEY,
6
7Name varchar (255),
8
9Class varchar (255),
10
11Contact No varchar (255),
12
13);