How Do I Create a Composite Primary Key in SQL Server 2008?

Creating Composite Primary Keys in SQL Server 2008

When designing a database in SQL Server 2008, it is sometimes necessary to define a composite primary key, which involves specifying multiple columns to form a unique identifier for each row. Understanding how to create a composite primary key is crucial for maintaining data integrity and ensuring efficient database operations.

Creating a Composite Primary Key

To create a composite primary key, follow these steps:

1. Declare the Data Table: Use the CREATE TABLE statement to define the structure of the table.
2. Define the Columns: Specify the names and data types of the columns that will participate in the composite primary key.
3. Use Composite Primary Key Syntax: After defining the columns, use the PRIMARY KEY keyword followed by the columns within parentheses to declare the composite primary key. The order of the columns in the parentheses is significant, as it determines the priority order for identifying unique rows.

Example:

Consider the following table:

CREATE TABLE MyTable (
     ColumnA INTEGER NOT NULL,
     ColumnB INTEGER NOT NULL,
     ColumnC VARCHAR(50)
);

To create a composite primary key using ColumnA and ColumnB:

ALTER TABLE MyTable ADD PRIMARY KEY (ColumnA, ColumnB);

After executing this statement, the specified combination of ColumnA and ColumnB values will be enforced as unique for each row in the MyTable.

Benefits of Composite Primary Keys:

• Data Integrity: Ensure that each row in the table is uniquely identifiable, reducing data duplication and inconsistencies.
• Query Optimization: Optimize query performance by using the primary key as an efficient index for retrieving data.
• Referential Integrity: Enable relationships with other tables by referencing the composite primary key in foreign key constraints.

The above is the detailed content of How Do I Create a Composite Primary Key in SQL Server 2008?. For more information, please follow other related articles on the PHP Chinese website!