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18 Απρ 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.
17 Σεπ 2020 · You can define a primary key in SQL Server 2012 by using SQL Server Management Studio or Transact-SQL. Creating a primary key automatically creates a corresponding unique, clustered or nonclustered index.
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).
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.
In this tutorial, you will learn about the primary key and how to use the SQL Server PRIMARY KEY constraint to create a primary key for a table.
16 Σεπ 2024 · SQL Server automatically creates indexes when PRIMARY KEY and UNIQUE constraints are defined on table columns. For example, when you create a table with a UNIQUE constraint, Database Engine automatically creates a nonclustered index.
4 Οκτ 2021 · A primary key is a constraint put on a column or columns in a table to guarantee each row in a table is unique. One aspect that makes a table relational is that it has unique rows. If there are two rows in a table with exactly the same data, that table is not considered relational.
