The primary key is a unique identifier that is comprised of a column or combination of columns with values that do not change over the life of the data in the row. Because uniqueness is essential to good database design, it is best to specify a primary key when you define the table.
It is recommended that you do not use approximate data types such as FLOAT and DOUBLE for primary keys or for columns with unique constraints. Approximate numeric data types are subject to rounding errors after arithmetic operations.
This section describes how to create and edit primary keys in your database. You can use either Sybase Central or Interactive SQL to perform these tasks.
Column order in multi-column primary keys
Primary key column order is determined by the primary key and foreign key clauses in the CREATE TABLE statement. It is not based on the order of the columns as specified in the primary key declaration of the CREATE TABLE statement.
Managing primary keys (Sybase Central)
Managing primary keys (SQL)