How Can I Create a Relational Table with Two Separate Auto-Incrementing Columns?

SQL: Creating a Relational Table with Two Distinct Auto Increments

Problem:

You want to create a relational table with two auto-incremented columns, but you encounter an error.

Explanation:

Your attempt to establish a relational table with multiple auto-incremented columns is based on a misunderstanding of the concept of a primary key.

Key Concepts:

• Primary key: A unique identifier that identifies each row in a table.
• Auto-increment: A feature that automatically generates a unique value for the specified column.

Mistake:

• Assigning the ID column as a primary key.
• Assuming that the ID column provides row uniqueness, which it does not.

Resolution:

1. Remove superfluous ID fields: Eliminate the ID columns from both tables since they are unnecessary for row identification.
2. Declare row uniqueness: Enforce row uniqueness by creating unique constraints on data-derived keys, such as a combination of name fields. For example:

CREATE TABLE relational_table (
    name_first CHAR(30), 
    name_last  CHAR(30),
    CONSTRAINT PK
        PRIMARY KEY ( name_last, name_first )
    )

3. Create associative table: To establish a relationship between the two tables, create an associative table that uses the primary keys from both tables as the primary key. For example:

CREATE TABLE user_sport (
    user_name  CHAR(16) NOT NULL,   -- FK
    sport_code CHAR(4)  NOT NULL,   -- FK
    start_date DATE     NOT NULL,

    CONSTRAINT PK 
        PRIMARY KEY ( user_name, sport_code )
    )

4. Remove auto-inc statements: Auto-increment is not necessary for relational tables and can lead to confusion.

Benefits of Removal:

• Enforces row uniqueness.
• Improves data integrity.
• Eliminates duplicate records.
• Simplifies foreign key relationships.

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