GUID vs UUID

What is a GUID vs UUID

The story is one of timing. When Microsoft added globally unique identifiers to COM in the early 1990s, the term GUID was already in use internally, and it stuck through OLE, Active Directory, the Windows registry and .NET. The RFC line of documents standardised the same structure as a UUID. Both describe a 128-bit number, and both are written as 32 hex digits in the 8-4-4-4-12 grouping. Convert one to the other and not a single bit changes.

What differs is presentation. Microsoft's ecosystem tends to write GUIDs in upper case and inside braces — {4C6E0549-82B1-47B0-9479-211A64583258} — because that is the format the .NET Guid.ToString("B") format specifier produces and the format SQL Server's management tools display. The RFC format is lower case with no braces. Parsers are case-insensitive and almost all accept the braced form, so this is cosmetic; but it is the reason two people can compare the same value and think they are looking at different things.

The one place the distinction is real is sort order. SQL Server's uniqueidentifier type compares the last six bytes before the rest, so ordering a column of GUIDs does not give you insertion order or alphabetical order — it gives you an order that looks random until you know the rule. This is a property of that column type, not of the GUID itself, and it is why a v7 GUID (or a BINARY(16) with your own comparison) matters when insertion order has to match index order.

How to

1. Need a value for a .NET Guid, a SQL Server column or a COM interface? Generate it here and paste it — braces and upper case are one checkbox away.
2. Comparing two identifiers that look different, one braced and one not? Strip the braces and hyphens and lower-case both before comparing; if the 32 hex digits match, the values are identical.
3. Storing GUIDs in SQL Server and ordering by them? Do not assume the order means anything. Add an explicit creation column, or use v7 values generated in the application.

Use cases

• .NET and Windows development, where the API surface says Guid and the tooling displays braces.
• SQL Server tables, where the column type is called uniqueidentifier and accepts either spelling.
• Cross-platform APIs, where the value leaves Microsoft's world and becomes a UUID again — the same bytes, a different label.

Compare GUID vs UUID with other formats

Code examples

C# / .NET

// random, equivalent to UUID v4
Guid a = Guid.NewGuid();

// time-ordered (v7), .NET 9+
Guid b = Guid.CreateVersion7();

// the three common string shapes
a.ToString("D");   // 4c6e0549-82b1-47b0-9479-211a64583258
a.ToString("B");   // {4c6e0549-82b1-47b0-9479-211a64583258}
a.ToString("N");   // 4c6e054982b147b09479211a64583258

// all three parse back to the same value
Guid.Parse(a.ToString("N")) == a;   // true

Python / anywhere else

import uuid

# This is what .NET calls a GUID.
u = uuid.uuid4()
print(u)         # 4c6e0549-82b1-47b0-9479-211a64583258
print(u.hex)     # 4c6e054982b147b09479211a64583258
print(u.bytes)   # b'Ln\x05I\x82\xb1G\xb0\x94y!\x1aeX2X'  (16 bytes)

# A braced string from .NET parses unchanged.
uuid.UUID('{4C6E0549-82B1-47B0-9479-211A64583258}')

SQL Server

-- generate
SELECT NEWID();                        -- random, equivalent to v4
SELECT NEWSEQUENTIALID();              -- ordered, only valid as a column default

-- compare without worrying about braces, case or hyphens
SELECT *
FROM   dbo.orders
WHERE  CONVERT(uniqueidentifier, @id) = order_id;

-- and remember: ORDER BY a uniqueidentifier column is not creation order

Frequently asked questions