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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).
To create a new table with a column defined as the primary key, you can use the keyword PRIMARY KEY at the end of the definition of that column. In our example, we create the table product using a CREATE TABLE clause, with the names of the columns and their respective data types in parentheses.
In this tutorial, you will learn about the primary key and how to use the SQL PRIMARY KEY constraint to add a primary key to the table
May 17, 2024 · SQL PRIMARY KEY Examples. Let’s look at some examples of the PRIMARY KEY Constraint in SQL, and understand it’s working. Create PRIMARY KEY in SQL Example. In this example, we will create primary key in a new table using CREATE TABLE statement. Query. CREATE TABLE Persons (PersonID int NOT NULL PRIMARY KEY, LastName varchar(255) NOT NULL,
In SQL, the PRIMARY KEY constraint is used to uniquely identify rows. It is a combination of NOT NULL and UNIQUE constraints i.e. it cannot contain duplicate or NULL values. Example. -- create Colleges table with primary key college_id CREATE TABLE Colleges ( college_id INT, college_code VARCHAR(20) NOT NULL, college_name VARCHAR(50),
Apr 18, 2024 · You can define a primary key in the SQL Server Database Engine by using SQL Server Management Studio or Transact-SQL. Creating a primary key automatically creates a corresponding unique clustered index. However, your primary key can be specified as a nonclustered index instead.
Jun 28, 2024 · This tutorial covers SQL Primary Key definitions, rules, How to add a primary key to an existing table in SQL, interesting facts, and more with detailed examples.
The basic syntax of adding PRIMARY KEY using CREATE TABLE and ALTER TABLE statements and dropping PRIMARY KEY using DROP TABLE statement is given below. CREATE TABLE Syntax. Single column Primary Key. The first CREATE table syntax is without using a constraint name and the second syntax is with a constraint name. Both are valid.
Primary Key can be created in two ways in SQL Server: Using T-SQL. Using SSMS (SQL Server Management Studio) Create Primary Key Using T-SQL. A primary key can be configured in the create table T-SQL script. Append CONSTRAINT statement at the end of all column declaration. Syntax: Primary Key.
A primary key is a column or a group of columns that uniquely identifies each row in a table. You create a primary key for a table by using the PRIMARY KEY constraint. If the primary key consists of only one column, you can define use PRIMARY KEY constraint as a column constraint: pk_column data_type PRIMARY KEY, ...
