Lesson Learned #393:Troubleshooting Azure SQL DataSync Error:Cannot Insert NULL Value into Column ID

In this blog article, we will delve into a common error encountered when synchronizing data with Azure SQL DataSync. We'll explore the error message "Error #1: SqlException Error Code: -2146232060 - SqlError Number: 515, Message: Cannot insert the value NULL into column 'ID', table 'dbo.Customers'; column does not allow nulls. INSERT fails. SqlError Number: 3621, Message: The statement has been terminated." We will provide a detailed explanation of the error and its possible causes, followed by a T-SQL code snippet that reproduces the error scenario.

Error Description: When synchronizing data with Azure SQL DataSync, you may come across an error indicating that a NULL value cannot be inserted into the 'ID' column of the 'dbo.Customers' table. The error message indicates that the column does not allow NULL values, causing the INSERT operation to fail. This error is accompanied by the statement termination message.

Error Message: Error #1: SqlException Error Code: -2146232060 SqlError Number: 515 Message: Cannot insert the value NULL into column 'ID', table 'dbo.Customers'; column does not allow nulls. INSERT fails. SqlError Number: 3621 Message: The statement has been terminated.

Explanation: The error message suggests that the 'ID' column in the 'dbo.Customers' table has a constraint that disallows NULL values. This means that whenever an INSERT statement is executed and a NULL value is provided for the 'ID' column, the operation will fail.

Possible Causes:

1. Missing or Incorrect Column Mapping: Ensure that the column mapping between the source and destination databases is correctly defined. If the 'ID' column in the source table allows NULL values while the destination table does not, this error can occur.

2. NULL Value in the Source Data: Check if the source data contains any NULL values for the 'ID' column. If the source data has NULL values, and the destination table does not allow NULLs, the synchronization process will encounter this error.

3. Data Type Mismatch: Verify that the data type of the 'ID' column is consistent between the source and destination databases. If there is a mismatch, such as attempting to insert a string value into an integer 'ID' column, the INSERT operation will fail.

4. Synchronization Conflict: It is possible that conflicting changes have been made to the 'ID' column in the source and destination databases. For example, if an ID value is generated in the source database but conflicts with an existing ID in the destination database, the synchronization will fail.

T-SQL Code Snippet: To reproduce the error scenario, you can use the following T-SQL code snippet:

By executing the above T-SQL code, you will encounter the same error, with the inability to insert a NULL value into the 'ID' column.

-- Create a sample table with a non-nullable 'ID' column
CREATE TABLE dbo.Customers
(
    ID INT NOT NULL,
    Name NVARCHAR(50)
)

-- Attempt to insert a NULL value into the 'ID' column
INSERT INTO dbo.Customers (ID, Name)
VALUES (NULL, 'John Doe')

Enjoy!