Why Am I Getting the 'Cannot Insert the Value NULL into Column 'id'' Error in SQL Server?

SQL Server's "Cannot Insert NULL into Column 'id'" Error: A Comprehensive Guide

Inserting data into an SQL Server database requires providing values for all columns, especially the primary key. If a column is designated as NOT NULL and lacks a default value, attempting to insert a NULL will trigger an error.

Scenario: Inserting into a Role Table

Consider this SQL statement:

<code class="language-sql">INSERT INTO role (name, created) VALUES ('Content Coordinator', GETDATE()), ('Content Viewer', GETDATE())</code>

This tries to add two rows to the role table (containing name and created columns – the latter with a default timestamp). The primary key column, id, is omitted.

Error Breakdown

SQL Server demands explicit primary key values or automatic generation. Since id isn't specified and has no default, SQL Server assigns it NULL. However, id is defined as NOT NULL, preventing NULL insertion. The resulting error message is:

<code>Msg 515, Level 16, State 2, Line 1
Cannot insert the value NULL into column 'id', table 'CMT_DEV.dbo.role'; column does not allow nulls. INSERT fails.
The statement has been terminated.</code>

Solution: Auto-Increment to the Rescue

The solution is to ensure id always receives a valid value. The most common method is using auto-increment:

Using SQL Server Management Studio (SSMS):

1. Open the role table in Design mode.
2. Select the id column and access its Column Properties.
3. Under "Identity Specification," set "Is Identity" to "Yes" and "Identity Increment" to 1.

This configures id to automatically increment for each new row, eliminating manual primary key specification.

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