How to Add GUID Column in SQL Server: GUIDs, Uniqueidentifier, NEWID, NEWSEQUENTIALID, and Best Practices 2026

How to add guid column in sql server: you can add a GUID column quickly and safely, even in large tables. Quick fact: adding a uniqueidentifier column with a default NEWID or NEWSEQUENTIALID is a common pattern to create a globally unique primary key or reference column. In this guide you’ll find a practical, step-by-step approach, plus best practices, potential pitfalls, and performance tips.

• Quick steps overview:
  1. Decide the purpose: primary key, unique reference, or a non-key GUID column.
  2. Choose default strategy: NEWID vs NEWSEQUENTIALID.
  3. Handle existing data: add as NULL if not required to be NOT NULL, then populate.
  4. Add constraints as needed: PRIMARY KEY, UNIQUE, or FOREIGN KEY considerations.
  5. Consider indexing and performance impact on large tables.
  6. Test in a staging environment before production.
• Common formats you’ll see in practice:
  • Step-by-step commands for T-SQL
  • Short checklist before applying changes
  • Quick rollback plan if something goes wrong
    Useful resources and references unlinked text, just plain names and URLs:
    Apple Website – apple.com
    Microsoft Docs – docs.microsoft.com
    SQL Server Tutorials – sqlservertutorial.net
    Stack Overflow Threads – stackoverflow.com
    SQL Server How-To – sql-server-tips.com
    GitHub SQL snippets – github.com

Understanding GUIDs and Use Cases

GUIDs Globally Unique Identifiers are 16-byte values designed to be unique across space and time. In SQL Server, the data type is uniqueidentifier. Use cases include:

• Brand-new primary keys when you don’t want to rely on IDENTITY columns
• Mallback references that need to be unique across databases
• Merging data from multiple sources without key collisions

Pros:

• Universally unique across tables and databases
• Can be generated client-side or server-side
• Reduces likelihood of key collisions during data merges

Cons:

• Larger than int/bigint keys, potentially bigger index size
• NOT SEQUENCED by default, which can cause index fragmentation if used as clustered primary key
• Slightly slower joins compared to integer keys in some scenarios

When to Add a GUID Column

• You’re migrating from another system that already uses GUIDs
• You want to decouple the primary key from the application’s data layer
• You need to merge data from multiple databases and avoid key collisions
• You require client-generated IDs e.g., offline scenarios

Adding a GUID Column: Step-by-Step Guide

Scenario A: Add a new GUID column with a default value for new rows

• Use case: You want every new row to automatically get a GUID.
• SQL steps:
  1. ALTER TABLE YourTable ADD MyGuidColumn uniqueidentifier NOT NULL CONSTRAINT DF_YourTable_MyGuidColumn DEFAULT NEWID;
  2. If you also want indexing, create a nonclustered index: CREATE INDEX IX_YourTable_MyGuidColumn ON YourTable MyGuidColumn;
• Notes:
  • NEWID generates a random GUID
  • NEWSEQUENTIALID generates sequential GUIDs which can improve index performance on inserts, but has limitations cannot be used as default with a column that is also used for replication or in some cross-database scenarios

Scenario B: Add a new GUID column without populating existing rows immediately How to add gifs to your discord server a step by step guide for reactions and channels 2026

• Use case: You need to add the column but want to backfill later.
• SQL steps:
  1. ALTER TABLE YourTable ADD MyGuidColumn uniqueidentifier NULL;
  2. Backfill existing rows in batches to avoid long locks:
     • UPDATE YourTable SET MyGuidColumn = NEWID WHERE MyGuidColumn IS NULL;
  3. After backfill, set NOT NULL and add a default if desired:
     • ALTER TABLE YourTable ALTER COLUMN MyGuidColumn uniqueidentifier NOT NULL;
     • ALTER TABLE YourTable ADD CONSTRAINT DF_YourTable_MyGuidColumn DEFAULT NEWID FOR MyGuidColumn;
• Tips:
  • For very large tables, backfill in manageable batches using TOP and a loop or a client-side script to avoid long-running transactions.

Scenario C: Add a GUID column as a PRIMARY KEY

• Use case: You want the GUID to be the primary key.
• SQL steps:
  1. If you already have a surrogate PK, adding a separate GUID as PK may require redesign; otherwise:
     • ALTER TABLE YourTable ADD Id uniqueidentifier NOT NULL CONSTRAINT DF_YourTable_Id DEFAULT NEWID;
     • ALTER TABLE YourTable ADD CONSTRAINT PK_YourTable_Id PRIMARY KEY NONCLUSTERED Id;
  2. If you can switch to clustered PK on the GUID for a more stable index, plan carefully:
     • Consider recreating the primary key and clustered index on Id
• Note: A GUID PK is often nonclustered to avoid fragmentation; use a separate integer as clustered key if performance is critical and GUIDs are used primarily as references.

Scenario D: Adding GUIDs for a relationship foreign keys

• Use case: You’re linking to a GUID-based key from a child table.
• SQL steps:
  1. Ensure the parent table has a GUID column with a stable default or pre-filled GUIDs.
  2. In the child table, add a column of type uniqueidentifier, optionally NOT NULL, and add a foreign key constraint:
     • ALTER TABLE ChildTable ADD ParentGuid uniqueidentifier NOT NULL;
     • ALTER TABLE ChildTable ADD CONSTRAINT FK_Child_Parent FOREIGN KEY ParentGuid REFERENCES ParentTableId;
• Tips:
  • Consider creating a cascading rule for deletes/updates if your domain requires it.

Performance and Index Considerations

• Indexing GUID columns:
  • Nonclustered indexes on GUID columns are common, but avoid making GUIDs the clustering key unless you have a specific reason.
  • Use NEWSEQUENTIALID if you want less page fragmentation on insert-heavy tables.
• Fragmentation and maintenance:
  • After adding a GUID column that becomes a primary key or part of a clustered index, monitor fragmentation and plan routine index rebuilds or reorganizes.
• Storage:
  • GUIDs take more storage than integers; plan accordingly for large tables with many affected indexes.

Practical Examples: Useful T-SQL Snippets

• Add a new GUID column with default NEWID:
  ALTER TABLE dbo.Orders ADD OrderGuid uniqueidentifier NOT NULL CONSTRAINT DF_Orders_OrderGuid DEFAULT NEWID;
  CREATE UNIQUE INDEX IX_Orders_OrderGuid ON dbo.OrdersOrderGuid;

• Add a nullable GUID column and backfill:
  ALTER TABLE dbo.Customers ADD CustomerGuid uniqueidentifier NULL;
  UPDATE dbo.Customers SET CustomerGuid = NEWID WHERE CustomerGuid IS NULL;
  ALTER TABLE dbo.Customers ALTER COLUMN CustomerGuid uniqueidentifier NOT NULL;
  ALTER TABLE dbo.Customers ADD CONSTRAINT DF_Customers_CustomerGuid DEFAULT NEWID FOR CustomerGuid;

• Add GUID as a foreign key target:
  ALTER TABLE dbo.Invoices ADD CustomerGuid uniqueidentifier NOT NULL;
  ALTER TABLE dbo.Invoices ADD CONSTRAINT FK_Invoices_Customers FOREIGN KEY CustomerGuid REFERENCES dbo.CustomersCustomerGuid; How to add games in discord server step by step guide: Add Games, Bots, and Fun 2026

• Using NEWSEQUENTIALID for better insert performance where appropriate:
  — Note: NEWSEQUENTIALID can only be used as a default for a column and cannot be replicated with IDENTITY behavior
  ALTER TABLE dbo.Orders ADD OrderGuid uniqueidentifier NOT NULL CONSTRAINT DF_Orders_OrderGuid DEFAULT NEWSEQUENTIALID;
  CREATE UNIQUE INDEX IX_Orders_OrderGuid ON dbo.OrdersOrderGuid;

Data Quality and Validation

• Enforce uniqueness as needed:
  • For GUID columns intended as keys or natural keys, add UNIQUE constraints or include in primary keys as appropriate.
• Validate existing data:
  • After backfilling, run queries to ensure there are no NULLs and that all existing rows have valid GUIDs.

Security Considerations

• GUIDs are not secrets by design; do not rely on them for security-sensitive purposes.
• If exposing GUIDs in URLs or APIs, consider obfuscation or hashing if needed, as GUIDs can be predictable in sequential modes.

Migration Strategy and Rollback

• Always back up your database or ensure a restore point exists before schema changes.
• For large tables, perform the change in maintenance windows or during low-traffic times.
• Rollback plan:
  • If you add a NOT NULL column with a default, you can drop constraints and the column if something goes wrong:
    • ALTER TABLE dbo.Orders DROP CONSTRAINT DF_Orders_OrderGuid;
    • ALTER TABLE dbo.Orders DROP COLUMN OrderGuid;
• Test in a staging environment to verify performance and correctness before production deployment.

Real-World Tips and Common Pitfalls

• Pitfall: Changing a GUID column that is part of a composite primary key can be complex; plan the key structure before making changes.
• Tip: If you expect heavy insert activity, consider using NEWSEQUENTIALID for better index performance, but avoid in scenarios requiring cross-database replication compatibility.
• Tip: Keep a consistent GUID generation strategy across all tables to simplify data merging and migrations.

Frequently Asked Scenarios and Quick Answers

• Should I use NEWID or NEWSEQUENTIALID by default?
  • NEWID gives random GUIDs, good for uniqueness across distributed systems. NEWSEQUENTIALID reduces index fragmentation on insert-heavy tables but has constraints not always suitable for every scenario.
• Can I add a GUID column to a table that already has data?
  • Yes. Add the column as NULL, backfill with NEWID, then alter to NOT NULL.
• Is a GUID primary key a good idea?
  • It can work well for distributed systems but may cause larger indexes and potential fragmentation if used as the clustered key. Consider using a separate integer surrogate as the clustered index and keep GUIDs as nonclustered keys if performance is a concern.
• How do I backfill GUIDs in batches?
  • Use a loop or a batching technique in your SQL script, updating a subset of rows at a time, and commit in chunks to avoid long-running transactions.
• How do I enforce uniqueness on a GUID column?
  • Add a UNIQUE constraint or use it as part of the PRIMARY KEY.
• How to handle GUIDs in a data warehouse vs transactional database?
  • GUIDs are great for merging data across sources in a data warehouse. In OLTP, consider the performance trade-offs and index strategy.
• Can I drop the GUID column later?
  • Yes, but ensure you drop any constraints or references to avoid errors.
• How do I verify the new GUID column was added correctly?
  • Run a quick check: SELECT TOP 1000 * FROM YourTable WHERE MyGuidColumn IS NULL; It should return none after NOT NULL is enforced.
• What about default values in existing rows?
  • If you backfilled, those existing rows will get GUIDs. New rows will have the default unless you override it.
• Do I need to rebuild indexes after adding a GUID column?
  • Rebuilding or reorganizing indexes may be beneficial, especially if the GUIDs become part of clustered or heavily used indexes.

Frequently Asked Questions

How do I add a GUID column with a default for new rows?

Add a new column with a default constraint using NEWID or NEWSEQUENTIALID, and, if needed, set it as NOT NULL.

Can I convert an integer ID to a GUID?

You generally cannot convert an existing integer primary key to a GUID without changing the data model, as you would need to recreate the primary keys and potentially migrate related data.

What are the performance implications of GUID keys?

GUIDs are larger and can cause wider indexes and more page splits. Use careful indexing strategy and consider NEWSEQUENTIALID to reduce fragmentation. How to add emojis to your discord server a step by step guide: Unicode vs Custom Emojis, Permissions, and Tips 2026

How do I ensure GUID values remain unique across related tables?

Use a single source of GUIDs, enforce foreign keys, and consider using the same GUID generation method across tables to preserve referential integrity.

Should I index GUID columns?

Yes, but avoid making every GUID column clustered. Nonclustered indexes on GUID columns are common; consider a thoughtful indexing plan.

How do I generate GUIDs for existing data?

Use NEWID to generate GUIDs for existing rows, then update all rows with a value if NULL.

What are the limitations of NEWSEQUENTIALID?

NEWSEQUENTIALID can’t be used with a column that’s part of a replicated publication in certain configurations and is not random, which might affect some use cases.

How can I backfill GUIDs efficiently?

Backfill in batches, using TOP with ORDER BY to avoid locking large portions of the table for too long. How To Add Days In SQL Server 2012 Master This Simple Query Now: DATEADD, EOMONTH, And Practical Day Arithmetic 2026

How do I remove a GUID column?

Drop any constraints first, then use ALTER TABLE ADD/DROP COLUMN, and handle any dependent objects like foreign keys.

What are real-world examples of GUID usage?

GUIDs are widely used for distributed systems, merging data from multiple sources, and creating unique keys across databases without coordination.

End of content

You add a GUID column in SQL Server by using the UNIQUEIDENTIFIER data type and setting a default constraint to NEWID or NEWSEQUENTIALID.

In this guide you’ll learn when to use GUIDs, how to add them to new and existing tables, how to populate and index them, and best practices. Here’s a quick outline to get you started: How to add date column in sql server its about time: A practical guide to adding date, datetime2, and defaults 2026

• Why GUIDs matter and when they’re overkill
• Choosing NEWID vs NEWSEQUENTIALID
• Adding GUIDs to new tables
• Adding GUIDs to existing tables step-by-step
• Indexing and constraints for GUID columns
• Practical examples and common pitfalls
• Real-world tips for distributed systems and data merges

Useful resources unclickable: Microsoft Docs – docs.microsoft.com, SQL Server Data Types – docs.microsoft.com/en-us/sql/t-sql/data-types/uniqueidentifier, DEFAULT constraints – docs.microsoft.com/en-us/sql/t-sql/statements/alter-table-transact-sql, GUID in SQL Server – en.wikipedia.org/wiki/Globally_unique_identifier

---

Why a GUID column and when it helps

A GUID Globally Unique Identifier is a 128-bit value that guarantees uniqueness across tables, databases, and even servers. In SQL Server, a GUID is stored as the data type UNIQUEIDENTIFIER and takes up 16 bytes per value.

Why consider GUIDs:

• You need unique keys across distributed systems or merges from multiple databases.
• You want to avoid coordination during key generation no sequence server needed at the time of insert.
• You’re building a system that requires offline data collection or replication without key collisions.

What to know before you start:

• GUIDs are larger than typical integer keys. This can affect storage, index size, and, in some workloads, latency.
• If you plan to cluster indexes on GUIDs, consider the access pattern. Random GUIDs can cause page fragmentation, leading to less efficient index seeks.

Key stats to keep in mind: How to Add Dank Memer to Your Discord Server a Step by Step Guide 2026

• GUID size: 16 bytes per value.
• Possible combinations: 2^128 ~3.4 x 10^38 unique values, which minimizes collision risk in large distributed systems.
• Index implications: Non-sequential GUIDs can lead to fragmentation; sequential GUIDs help reduce this.

Best-fit scenarios:

• Distributed apps where you generate IDs on clients or offline devices.
• Systems that merge data from multiple sources without key collisions.
• Situations where you don’t want to coordinate ID generation across services.

---

NEWID vs NEWSEQUENTIALID: which should you choose?

Feature	NEWID	NEWSEQUENTIALID
GUID style	Random, highly dispersed values	Sequentially increasing values still GUIDs
Fragmentation impact	Higher potential if used as a clustered key	Lower fragmentation when used as a clustered key
Performance for inserts	Generally fine, but index pages can churn	Better insert performance in clustered indexes due to locality
Use case	General-purpose GUIDs for unique keys	GUIDs where you want better write-order locality e.g., primary keys on clustered index

Tips:

• If you’re creating a new table and plan to use the GUID as the primary key and it’s the clustered index, NEWSEQUENTIALID can help with page locality and performance.
• If you need maximum randomness e.g., to avoid guessable IDs or to distribute values evenly across shards, NEWID is fine.
• You can mix: you can generate a GUID with NEWSEQUENTIALID as a default, and still fill older rows with NEWID if needed but keep it consistent where possible for performance.

Practical takeaway:

• For most new designs that require a GUID primary key, prefer NEWSEQUENTIALID to reduce fragmentation. If you’re populating GUIDs from application code or want more randomness, NEWID is perfectly acceptable.

---

Add a GUID column to a new table

When you create a new table and want the primary key or a GUID column to auto-generate values, you can define it with a default:

CREATE TABLE dbo.Orders

    OrderId UNIQUEIDENTIFIER NOT NULL DEFAULT NEWID,
    CustomerName NVARCHAR100 NOT NULL,
    OrderDate DATETIME2 NOT NULL DEFAULT SYSUTCDATETIME,
    PRIMARY KEY OrderId
;

If you prefer sequential GUIDs: How To Add Client PC To Domain In Windows Server 2012 Step By Step Guide 2026

CREATE TABLE dbo.Shipments

    ShipmentId UNIQUEIDENTIFIER NOT NULL DEFAULT NEWSEQUENTIALID,
    ShipmentDate DATETIME2 NOT NULL DEFAULT SYSUTCDATETIME,
    Destination NVARCHAR150 NOT NULL,
    PRIMARY KEY ShipmentId
;

Notes:

• The DEFAULT constraint ensures that every new row gets a GUID without extra application logic.
• The primary key on the GUID column is a clustered index by default unless you specify otherwise. If you plan to use a different clustering key, be mindful of how that impacts performance.

---

Add a GUID column to an existing table step-by-step

If you already have a table and want to introduce a GUID column for new and existing rows, follow these steps:

Step 1: Add a nullable GUID column to avoid violating NOT NULL during the transition

ALTER TABLE dbo.ExistingTable
ADD GuidColumn UNIQUEIDENTIFIER NULL;

Step 2: Populate the new column for existing rows

UPDATE dbo.ExistingTable
SET GuidColumn = NEWID;

Step 3: Enforce NOT NULL and add a default for future inserts
Option A: Default and NOT NULL How to Add Custom Emojis to Your Discord Server Step by Step Guide 2026

ALTER TABLE dbo.ExistingTable
ALTER COLUMN GuidColumn UNIQUEIDENTIFIER NOT NULL;

ALTER TABLE dbo.ExistingTable
ADD CONSTRAINT DF_ExistingTable_GuidColumn DEFAULT NEWID FOR GuidColumn;

Option B: Use NEWSEQUENTIALID for lower fragmentation

ALTER TABLE dbo.ExistingTable
ADD GuidColumn UNIQUEIDENTIFIER NOT NULL CONSTRAINT DF_ExistingTable_GuidColumn DEFAULT NEWSEQUENTIALID;

Notes:

• If you want the GUID column to be the primary key, you can add a primary key constraint after filling the data:

ALTER TABLE dbo.ExistingTable
ADD CONSTRAINT PK_ExistingTable_GuidColumn PRIMARY KEY CLUSTERED GuidColumn;

• If you use NEWSEQUENTIALID, ensure it’s supported by your SQL Server version and the column is defined with NOT NULL and a default constraint.

Alternative approach single statement, with caution:
Some people try to add a non-null column with a default in one step, relying on the default to fill existing rows. However, for clarity and to avoid surprises, the 3-step approach add NULL, populate, then enforce NOT NULL and default is usually safer.

---

Indexing GUID columns and best practices

• Primary keys: If you assign the GUID to be the primary key, you’ll inherently get a clustered index by default. If you choose a different clustering key, you’ll want to decide carefully based on your queries.
• Index size: GUIDs consume more storage than integers. Expect bigger index sizes and potentially longer index scans.
• Fragmentation: Use NEWSEQUENTIALID when possible to reduce page fragmentation in clustered indexes.
• Non-clustered indexes: If you frequently search by GUID in combination with other columns, adding non-clustered indexes on GUID or on GUID plus other keys can help.
• Compression: Consider row and page compression if storage is a concern and you’re on a version of SQL Server that supports it.

Example: create a non-clustered index on a GUID column

CREATE UNIQUE NONCLUSTERED INDEX IX_Orders_GuidColumn ON dbo.Orders OrderId;

Guidance for design decisions: How to add bots to your discord server on pc the ultimate guide to Setup, Permissions, and Tips 2026

• If you expect massive growth, and your GUIDs will be the primary keys, plan ahead for index maintenance and potential fragmentation.
• For tables with high insert throughput, prefer NEWSEQUENTIALID for the primary key column.
• If you’re merging data from multiple systems, GUIDs help avoid collision across sources.

---

Practical examples and common scenarios

Scenario A: New table with GUID primary key

• Perfect for distributed systems where you create IDs client-side and then push to the server.

Scenario B: Existing table needs a GUID key for replication or merges

• Follow the 3-step approach described above to minimize downtime and ensure data integrity.

Scenario C: GUIDs in data warehouses or ETL pipelines

• Use GUIDs as natural keys in staging areas when merging data from multiple sources, then map them to surrogate keys in fact tables as needed.

Scenario D: Hybrid approach

• Use an integer identity as the main primary key for performance, and add a separate GUID column with a UNIQUE constraint to support merging and distributed replication scenarios.

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• If you’re storing GUIDs in a clustered index, consider how your workload looks. Some teams keep a separate surrogate key int or bigint as the clustered key for performance, while the GUID acts as a unique, globally unique reference.

---

Data integrity and constraints

• Unique constraint: If you don’t want the GUID to be the primary key, you can enforce uniqueness with a UNIQUE constraint:

ALTER TABLE dbo.YourTable ADD CONSTRAINT UQ_YourTable_GuidColumn UNIQUE GuidColumn;

• Default constraints: Use a named default constraint so you can drop or alter it easily later.

---

Performance tips and pitfalls to avoid

• Avoid using a GUID as the only clustering key if your insert pattern is random. Prefer NEWSEQUENTIALID for the clustering key or keep a separate integer identity as the clustering key.
• Keep in mind GUIDs increase index size and can impact I/O. Monitor with SQL Server DMVs and query plans to verify impact.
• Use columnar compression or page compression if you’re on SQL Server with support for those features and your storage is at a premium.
• Test in a staging environment with realistic workloads to measure latency and index maintenance costs.

---

Real-world best practices

• Use GUIDs when you must merge data from multiple sources or create globally unique identifiers without a central authority.
• Prefer NEWSEQUENTIALID for clustered indexes to minimize fragmentation and improve insert performance.
• If possible, keep an integer surrogate key for the primary key and store GUIDs as a separate column with a UNIQUE constraint to support distributed systems without sacrificing performance.
• Document the choice in your data model so future developers understand why GUIDs were used in a particular way.

---

Frequently Asked Questions

What is a GUID in SQL Server?

A GUID in SQL Server is a 128-bit value stored as the UNIQUEIDENTIFIER data type. It ensures global uniqueness across databases and servers.

Should I use NEWID or NEWSEQUENTIALID for my GUID column?

If you care about write performance and index fragmentation, use NEWSEQUENTIALID for the GUID column that’s part of a clustered index. If you need maximum randomness, use NEWID.

How do I add a GUID column to an existing table?

1. Add a nullable GUID column.
2. Populate existing rows with NEWID.
3. Alter the column to NOT NULL and add a default constraint NEWID or NEWSEQUENTIALID.

Can a GUID be the primary key?

Yes, but consider indexing implications. GUIDs as primary keys, especially if randomly generated, can cause fragmentation. NEWSEQUENTIALID helps mitigate this.

How much space does a GUID take?

A GUID uses 16 bytes. When used as a primary/clustered key, you’ll see larger index sizes than integer keys.

How do I populate existing rows with GUIDs?

Use an UPDATE statement:
UPDATE dbo.YourTable SET GuidColumn = NEWID; How To Add A User In Windows Server 2008 R2 Standard Step By Step Guide 2026

How do I create a GUID column with a default in one shot?

Create the column with a DEFAULT constraint:
ALTER TABLE dbo.YourTable ADD GuidColumn UNIQUEIDENTIFIER NOT NULL DEFAULT NEWID;

Are GUIDs random-friendly for distribution keys?

Yes, especially when you want non-sequential, globally unique keys across distributed systems.

How to optimize GUID indexing?

Consider NEWSEQUENTIALID for the primary key, create nonclustered indexes on GUID columns as needed, and avoid using GUIDs as the sole clustering key if possible.

What are the trade-offs of using GUIDs in a data warehouse?

GUIDs are great for merging data from multiple sources, but their size and indexing can increase storage and potentially slow down certain queries. Plan with staging tables and surrogate keys when appropriate.

How do GUIDs affect replication?

GUIDs simplify merge replication scenarios because keys remain unique across publishers. Always test replication topology with GUIDs in your environment. How to Add Bots to Discord Server a Step by Step Guide for Your Community 2026

Can I generate GUIDs in the application code?

Yes. Generating GUIDs client-side can reduce latency, but you’ll need to ensure consistency with server-side defaults and constraints when the data is saved.

---

Resources and further reading

• Microsoft SQL Server Documentation – data types and UNIQUEIDENTIFIER basics
• SQL Server Default Constraints and ALTER TABLE syntax
• GUIDs in distributed systems and performance considerations
• Best practices for primary keys, clustering, and indexing in SQL Server
• Global unique identifiers GUIDs overview and usage patterns

Sources:

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