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SQL Anywhere 11.0.1 » SQL Anywhere Server - SQL Usage » Creating Databases » Ensuring data integrity » Using column defaults

 

The NEWID default

Universally Unique Identifiers (UUIDs), also known as Globally Unique Identifiers (GUIDs), can be used to identify unique rows in a table. The values are generated such that a value produced on one computer will not match that produced on another. They can therefore be used as keys in replication and synchronization environments.

Using UUID values as primary keys has some tradeoffs when you compare them with using GLOBAL AUTOINCREMENT values. For example:

  • UUIDs can be easier to set up than GLOBAL AUTOINCREMENT, since there is no need to assign each remote database a unique database ID. There is also no need to consider the number of databases in the system or the number of rows in individual tables. The Extraction utility (dbxtract) can be used to deal with the assignment of database IDs. This isn't usually a concern for GLOBAL AUTOINCREMENT if the BIGINT data type is used, but it needs to be considered for smaller data types.

  • UUID values are considerably larger than those required for GLOBAL AUTOINCREMENT, and will require more table space in both primary and foreign tables. Indexes on these columns will also be less efficient when UUIDs are used. In short, GLOBAL AUTOINCREMENT is likely to perform better.

  • UUIDs have no implicit ordering. For example, if A and B are UUID values, A > B does not imply that A was generated after B, even when A and B were generated on the same computer. If you require this behavior, an additional column and index may be necessary.

See also