Why Can't I Insert a Value into an Identity Column, and How Do I Fix It?

Troubleshooting the "Cannot Insert Explicit Value for Identity Column" Error

When you try to manually insert a value into an identity column (a column automatically assigned unique sequential values by the database), you'll encounter the error "Cannot insert explicit value for identity column in table 'table' when IDENTITY_INSERT is set to OFF." This happens because identity columns are designed to self-manage their values.

The Solution: Temporarily Enabling IDENTITY_INSERT

The solution is to temporarily enable IDENTITY_INSERT for the specific table. This setting overrides the automatic value generation. Here's the process:

1. Enable IDENTITY_INSERT: Use the following SQL command, replacing TableName with your table's name:

<code class="language-sql">SET IDENTITY_INSERT TableName ON</code>

2. Perform the INSERT: Now you can execute your INSERT statement with the explicit value for the identity column. For example:

<code class="language-sql">INSERT INTO TableName (IdentityColumnName, Column2, Column3)
VALUES (100, 'Some Value', 'Another Value');</code>

3. Disable IDENTITY_INSERT: Crucially, after the insertion, disable IDENTITY_INSERT to restore the automatic identity column behavior:

<code class="language-sql">SET IDENTITY_INSERT TableName OFF</code>

Illustrative Example:

Consider a table Orders with an identity column OrderID. To insert a record with a specific OrderID, you would do this:

<code class="language-sql">SET IDENTITY_INSERT Orders ON;

INSERT INTO Orders (OrderID, CustomerID, OrderDate)
VALUES (12345, 1, '2024-03-08');

SET IDENTITY_INSERT Orders OFF;</code>

This allows you to insert the value 12345 into the OrderID column. Remember to always disable IDENTITY_INSERT after your insertion to maintain the integrity of your identity column.

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