Table design concepts

When designing tables, you must be familiar with some related concepts.

Data types and table columns
When you create your table, you must indicate what type of data each column will store. By thinking carefully about the nature of the data you are going to be managing, you can set your tables up in a way that will give you optimal query performance, minimize physical storage requirements, and provide you with specialized capabilities for manipulating different kinds of data, such as arithmetic operations for numeric data, or comparing date or time values to one another.
Generated columns
A generated column is defined in a table where the stored value is computed using an expression, rather than being specified through an insert or update operation.
Hidden columns
When a table column is defined with the implicitly hidden attribute, that column is unavailable unless it is explicitly referenced. For example, if a SELECT * query is run against a table, implicitly hidden columns are not returned in the result table. An implicitly hidden column can always be referenced explicitly wherever a column name can be specified.
Auto numbering and identifier columns
An identity column provides a way for Db2® to automatically generate a unique numeric value for each row that is added to the table.
Constraining column data with constraints, defaults, and null settings
Data often must adhere to certain restrictions or rules. Such restrictions might apply to single pieces of information, such as the format and sequence numbers, or they might apply to several pieces of information.
Primary key, referential integrity, check, and unique constraints
Constraints are rules that limit the values that can be inserted, deleted, or updated in a table.
Unicode table and data considerations
The Unicode character encoding standard is a fixed-length, character encoding scheme that includes characters from almost all of the living languages of the world.

Parent topic: Designing tables

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