How to fix Error 2749 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 2749 – “Identity column must be of data type int”

Why This Error Happens

This error occurs when you attempt to define a column with the IDENTITY property using a data type other than int, bigint, smallint, tinyint, decimal, or numeric (with a scale of 0). SQL Server 2025 strictly enforces this rule because the identity property relies on integer-based seed and increment arithmetic, which is incompatible with data types like varchar, float, or date. This typically happens during table creation scripts, migration from another database platform, or when a developer mistakenly applies the identity property to a GUID or string-based primary key column.

Step-by-Step Resolution Guide

Step 1: Identify the Offending Column Definition

  • Locate the specific CREATE TABLE or ALTER TABLE script that triggered Error 2749.
  • Check the column definition; look specifically for syntax like CustomerID VARCHAR(10) IDENTITY(1,1).
  • Run the following query to find existing problematic tables in the database:
  SELECT t.name AS TableName, c.name AS ColumnName, ty.name AS DataType
  FROM sys.columns c
  JOIN sys.tables t ON c.object_id = t.object_id
  JOIN sys.types ty ON c.user_type_id = ty.user_type_id
  WHERE c.is_identity = 1;

Step 2: Correct the Data Type in the Script

  • Modify the script to use a valid integer-based data type.
  • Change the data type to INT if you expect fewer than 2.1 billion rows:
  CustomerID INT IDENTITY(1,1) PRIMARY KEY
  • Alternatively, use BIGINT if you anticipate exceeding the standard integer limit:
  CustomerID BIGINT IDENTITY(1,1) PRIMARY KEY

Step 3: Handle Existing Tables with Incorrect Types

  • If the table already exists with the wrong data type, you cannot simply ALTER the column to add an identity property; you must recreate the table structure.
  • Create a new staging table with the correct INT or BIGINT identity column.
  • Migrate the data using an INSERT INTO ... SELECT statement, then rename the tables to swap them into production.

Step 4: Address GUID or Unique Identifier Use Cases

  • If your business logic requires a non-integer unique value (like a GUID), do not use the IDENTITY property.
  • Use the UNIQUEIDENTIFIER data type combined with the DEFAULT NEWID() constraint instead:
  CustomerGUID UNIQUEIDENTIFIER DEFAULT NEWID()

Alternative or Verification Steps

  • Verification: Re-run the CREATE TABLE script in SQL Server Management Studio (SSMS) 21 or Azure Data Studio; confirm the table appears in the Object Explorer without throwing Error 2749.
  • Alternative: If integer-based auto-incrementing isn’t suitable for your schema, consider using a SEQUENCE object instead of an IDENTITY column, as sequences support a wider range of data types and offer more flexible control over value generation.