Subscribe to RSS
In SQL Server, a uniqueidentifier is just another data type, like int, varchar, etc., but its characteristics make it suitable as a primary key. It is much larger than a typical auto-increment integer, but it makes replication and migration much easier - data from two previously unrelated databases will not produce collisions on the primary keys if you use GUIDs, because each GUID is . Jun 17, · According to Wikipedia, a universally unique identifier (UUID) — also known as a globally unique identifier (GUID) — is a bit value (16 bytes) that is intended to be unique across multiple environments and timespans, and generated without needing a central repository. In theory (because it’s impossible to test), bits is wide enough to ensure a unique value for any GUID as .
Join Stack Overflow to learn, share knowledge, and build your career. Connect and share knowledge what is uniqueidentifier in sql server a single location that is structured and easy to search. In SQL server there is a type uniqueidentifier? What is this? What does it do? What is the difference between this and using primary key. It is a GUID column. This ensures that the value is unique and not only on this computer but over all the computers on the world.
As pointed out by tdammers in the comments section new GUIDs are not automatically generated when inserting rows but this effect could be achieved by defining newid as default value for the column. To further reduce the likelyhood of collisions, most GUID generators include some value that uniquely identifies the host in the hashing process, such as the primary NIC's MAC address, and maintain a machine-wide counter to avoid collisions between GUIDs generated on the same machine.
In SQL Server, a uniqueidentifier is just another data type, like intvarcharhow to improve torque and horsepower. It is much larger than a typical auto-increment integer, but it makes replication and migration much easier - data from two previously unrelated databases will not produce collisions on the primary keys if you use GUIDs, because each GUID is conceptually globally unique.
With auto-incrementing primary keys, you will certainly get overlaps, because both tables once started at 1, and modifying the primary key values means you also have to modify any foreign key values referencing this record. It can be done, but it's much harder than simply using GUIDs.
You need to keep apart the primary key which is a logical construct - it uniquely identifies your rows, it has to be unique and stable and NOT NULL. A GUID works well for a primary key, too - since it's guaranteed to be unique. The clustering key in SQL Server is a physical construct is used for the what is uniqueidentifier in sql server ordering of the data, and is a lot more difficult to get right.
A GUID is a horribly bad choice for a clustering key, since it's wide, totally random, and thus leads to bad index fragmentation and poor performance. Also, the clustering key row s is also stored in each and every what is uniqueidentifier in sql server of each and every non-clustered additional index, so you really want to keep it small - GUID is 16 byte vs.
In SQL Server, your primary key is by default your clustering key - but it doesn't have what instrument should i play test be.
Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. What is uniqueidentifier type? Ask Question. Asked 10 years, 3 months ago. Active 10 years, 3 months ago. Viewed 2k times. Improve this question. Add a comment. Active Oldest Votes. UPDATE: As pointed out by tdammers in the comments section new GUIDs are not automatically generated when inserting rows but this effect could be achieved by defining newid as default value for the column.
Improve this answer. Darin Dimitrov Darin Dimitrov k gold badges silver badges bronze badges. It doesn't automatically generate one unless you tell it to. I will update my answer. Thanks for pointing this out. Ever-increasing clustering key - how do you update your tomtom Clustered Index Debate Sign up or log in Sign up using Google.
Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Understanding quantum computing through drunken walks. Podcast How to build and maintain online communities, from gaming to…. Featured on Meta. Stack Overflow for Teams is now free for up to 50 users, forever.
Table of Contents
Mar 12, · Generally Uniqueidentifier is a 36 bit alphanumeric unique Value that will not be duplicated. Its syntax is XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX. It is a data type in SQLServer & it will be mostly. UNIQUEIDENTIFIER is a datatype. Datatypes define the nature of the data that they (i.e. columns and variables of this type) can contain (e.g. min / max values, etc) and certain behaviors of the data (e.g. how to handle comparisons). This particular datatype merely holds GUID / UUID values. sql-server performance sql-server database-design guid. Share. Improve this question. Follow I believe UNIQUEIDENTIFIER was added in SQL Server , so it's possible this application was originally written for SQL Server 7, which didn't support it. But that's just a guess, of course.
A column or local variable of uniqueidentifier data type can be initialized to a value in the following ways:. Comparison operators can be used with uniqueidentifier values. However, ordering is not implemented by comparing the bit patterns of the two values.
No other arithmetic operators can be used. Merge replication and transactional replication with updating subscriptions use uniqueidentifier columns to guarantee that rows are uniquely identified across multiple copies of the table.
The uniqueidentifier type is considered a character type for the purposes of conversion from a character expression, and therefore is subject to the truncation rules for converting to a character type.
That is, when character expressions are converted to a character data type of a different size, values that are too long for the new data type are truncated. See the Examples section. The following example converts a uniqueidentifier value to a char data type. The following example demonstrates the truncation of data when the value is too long for the data type being converted to.
Because the uniqueidentifier type is limited to 36 characters, the characters that exceed that length are truncated. Skip to main content. Contents Exit focus mode. Is this page helpful? Yes No. Any additional feedback? Skip Submit.