Sybase DC38133-01-0902-01 manual Declaring default global autoincrement

You assign each copy of the database a unique global database identification number. Adaptive Server Anywhere supplies default values in a database only from the partition uniquely identified by that database’s number.

For example, if you assigned the database in the above example the identity number 10, the default values in that database would be chosen in the range 10001–11000. Another copy of the database, assigned the identification number 11, would supply default value for the same column in the range 11001–12000.

Declaring default global autoincrement

You can set default values in your database by selecting the column properties in Sybase Central, or by including the DEFAULT GLOBAL AUTOINCREMENT phrase in a TABLE or ALTER TABLE statement.

Optionally, the partition size can be specified in parentheses immediately following the AUTOINCREMENT keyword. The partition size may be any positive integer, although the partition size is generally chosen so that the supply of numbers within any one partition will rarely, if ever, be exhausted.

For columns of type INT or UNSIGNED INT, the default partition size is 216 = 65536; for columns of other types the default partition size is 232 = 4294967296. Since these defaults may be inappropriate, especially if our column is not of type INT or BIGINT, it is best to specify the partition size explicitly.

For example, the following statement creates a simple table with two columns: an integer that holds a customer identification number and a character string that holds the customer’s name.

CREATE TABLE customer (

id INT DEFAULT GLOBAL AUTOINCREMENT (5000),

name VARCHAR(128) NOT NULL, PRIMARY KEY (id)

)

In the above example, the chosen partition size is 5000.

☞For more information on GLOBAL AUTOINCREMENT, see “CREATE TABLE statement” [ASA SQL Reference, page 407].

Setting the Global_database_id value

When deploying an application, you must assign a different identification number to each database. You can accomplish the task of creating and distributing the identification numbers by a variety of means. One method is to place the values in a table and download the correct row to each database based on some other unique property, such as user name.

130