SQL Server Error 8169

Error number

8169

Severity

16 (user-correctable error)

State

2

Product

Microsoft SQL Server Database Engine

Versions

All supported SQL Server versions (2016 to 2025), Azure SQL Database, Azure SQL Managed Instance

Category

Data Type & Conversion

Last reviewed

24 October 2026

What it means

Error 8169 means a piece of text had to become a uniqueidentifier (GUID) and is not in a GUID format SQL Server accepts, for example a placeholder, an empty string or 32 hex digits without hyphens.

A uniqueidentifier is written as 32 hexadecimal digits in groups of 8, 4, 4, 4 and 12, separated by hyphens, optionally inside braces: 6F9619FF-8B86-D011-B42D-00C04FC964FF. When text meets a uniqueidentifier, in a CAST, an INSERT into a GUID column, a comparison in WHERE or a parameter, SQL Server parses it. If it does not fit that pattern, the statement fails at run time with 8169 at severity 16. Like other conversion errors it does not quote the offending value, so you have to find the row.

The parser is strict about the start of the string and lenient about the end. A leading space, a missing hyphen or a letter outside A to F fails; braces are accepted; and in our tests characters after a valid 36-character GUID were ignored rather than rejected. So a clean result does not prove the input was clean. Because data type precedence converts the text side, a comparison such as WHERE device_id = @search fails on the first bad search string even if no row would match.

Common causes

• Placeholder values such as N/A, none or the string NULL in a varchar column loaded into a uniqueidentifier column.
• GUIDs written without hyphens (the 32-digit format many APIs and .NET ToString("N") produce).
• An empty string from a web form or API sent as a GUID parameter or compared with a GUID column.
• Leading spaces, quotes or other wrapping characters left over from a CSV import.
• A search box that compares whatever the user typed with a uniqueidentifier column.

Diagnose it

Read-only These queries only read metadata and dynamic management views. They do not change data, permissions or configuration, so they are safe to run first.

SELECT device_ref
FROM dbo.Staging
WHERE device_ref IS NOT NULL
  AND TRY_CONVERT(uniqueidentifier, device_ref) IS NULL;

SELECT LEN(device_ref) AS text_length,
       DATALENGTH(device_ref) AS bytes,
       COUNT(*) AS row_count,
       MIN(device_ref) AS sample
FROM dbo.Staging
WHERE TRY_CONVERT(uniqueidentifier, device_ref) IS NULL
GROUP BY LEN(device_ref), DATALENGTH(device_ref)
ORDER BY row_count DESC;

How to fix it

Each fix is labelled with what it changes. Try read-only checks and the least invasive fix first, and test changes outside production.

INSERT INTO dbo.Readings (device_id)
SELECT TRY_CONVERT(uniqueidentifier, device_ref)
FROM dbo.Staging
WHERE TRY_CONVERT(uniqueidentifier, device_ref) IS NOT NULL;

DECLARE @raw varchar(32) = '6F9619FF8B86D011B42D00C04FC964FF';
SELECT CONVERT(uniqueidentifier,
       STUFF(STUFF(STUFF(STUFF(@raw, 9, 0, '-'), 14, 0, '-'), 19, 0, '-'), 24, 0, '-')) AS device_id;

DECLARE @search varchar(50) = '';
SELECT name
FROM dbo.Devices
WHERE device_id = TRY_CONVERT(uniqueidentifier, NULLIF(@search, ''));

Examples

Loading a staging column that contains N/A

SET NOCOUNT ON;
CREATE TABLE dbo.Staging (device_ref VARCHAR(50));
INSERT INTO dbo.Staging VALUES ('6F9619FF-8B86-D011-B42D-00C04FC964FF'), ('N/A');
CREATE TABLE dbo.Readings (device_id UNIQUEIDENTIFIER);

INSERT INTO dbo.Readings (device_id)
SELECT device_ref FROM dbo.Staging;   -- 'N/A' is not a GUID

Msg 8169, Level 16, State 2, Line 6
Conversion failed when converting from a character string to uniqueidentifier.

A GUID without hyphens

SELECT CAST('6F9619FF8B86D011B42D00C04FC964FF' AS uniqueidentifier) AS device_id;

Msg 8169, Level 16, State 2, Line 1
Conversion failed when converting from a character string to uniqueidentifier.

An empty search value compared with a GUID column

SET NOCOUNT ON;
CREATE TABLE dbo.Devices (device_id UNIQUEIDENTIFIER PRIMARY KEY, name NVARCHAR(50));
INSERT INTO dbo.Devices VALUES ('6F9619FF-8B86-D011-B42D-00C04FC964FF', N'Till 1');

DECLARE @search varchar(50) = '';   -- nothing typed in the search box
SELECT name FROM dbo.Devices WHERE device_id = @search;

Msg 8169, Level 16, State 2, Line 6
Conversion failed when converting from a character string to uniqueidentifier.

How to prevent it

Keep GUIDs typed as uniqueidentifier from the application to the table: parameters, staging columns and variables. Validate text input at the boundary with TRY_CONVERT, and decide explicitly what happens to values that fail instead of letting the first bad row stop a load.

Agree on one textual format (36 characters with hyphens) with every system that sends you identifiers. For when to use GUID keys at all, see SQL data types explained.

Common questions

Learn more on CodeWithSQL

• CONVERT()
• CAST()
• SQL data types explained

Official documentation

• uniqueidentifier (Transact-SQL)
• TRY_CONVERT (Transact-SQL)
• Database Engine events and errors 8000 to 8999

Last technically reviewed 24 October 2026; examples and diagnostics run on SQL Server 2025 (17.0.1145.4). Message text checked against the engine's sys.messages catalogue.