Why Does SQL Server Throw a 'Null Value Insertion into Non-Nullable Column' Error, and How Can I Fix It?

Solving SQL Server's "Null Value Insertion" Error in Non-Nullable Columns

Inserting data into an SQL Server table might trigger this error:

<code>Cannot insert the value NULL into column 'id', table 'CMT_DEV.dbo.role'; column does not allow nulls. INSERT fails.</code>

This happens when you try to insert a NULL value into a column (like 'id', often a primary key) that's defined as NOT NULL. SQL Server can't insert NULL because no default value is specified for that column.

The Fix: Auto-Incrementing IDs

The solution is to automatically generate values for the 'id' column. The best approach is to use auto-increment.

Implementing Auto-Increment in SQL Server Management Studio:

1. Open your table in Design mode.
2. Select the 'id' column. Go to its properties.
3. In the "Identity Specification" section, set "Is Identity" to "Yes" and "Identity Increment" to 1.

This setup ensures SQL Server automatically assigns unique, sequential numbers to the 'id' column during inserts, eliminating the NULL value issue.

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