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Learn how to create, name and drop a PRIMARY KEY constraint on a table using SQL. A PRIMARY KEY constraint uniquely identifies each record in a table and can consist of single or multiple columns.
18 Απρ 2024 · Learn how to define a primary key in the SQL Server Database Engine by using SQL Server Management Studio or Transact-SQL. See examples, limitations, permissions, and related content for creating primary keys.
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, ...
CREATE TABLE T1 ( c1 INT PRIMARY KEY, c2 VARCHAR(50) SPARSE NULL, c3 INT SPARSE NULL, CSet XML COLUMN_SET FOR ALL_SPARSE_COLUMNS ); Q. Create a system-versioned disk-based temporal table. Applies to: SQL Server 2016 (13.x) and later, and Azure SQL Database.
A PRIMARY KEY can be defined on a column or multiple columns while creating a table or later. It is also possible to drop a PRIMARY KEY in a table if not required. SQL Server PRIMARY KEY Syntax. 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.
22 Ιουλ 2024 · When you specify a primary key constraint for a table, the Database Engine enforces data uniqueness by automatically creating a unique index for the primary key columns. This index also permits fast access to data when the primary key is used in queries.
5 Αυγ 2019 · This article demonstrates how to add a primary key to an existing table in SQL Server using Transact-SQL. A primary key is a column that has been configured as the unique identifier for a given table. You would normally create a primary key constraint when you create the table, but you can also add a primary key to an existing table.
