13.7 Specifying the FIX attribute
(1) Effects of specifying the FIX attribute
The effects of specifying the FIX attribute for a table are discussed as follows.
- Improved performance
- The performance of retrieving a specific column becomes constant regardless of the order of the column definitions. Additionally, the column retrieval time is reduced, compared to when the FIX attribute is not specified.
- Access performance is improved even when there are many columns because a UAP can use an interface for each row.
- Improved operability
- If the null value is found in the input data when a column of a table with the FIX attribute is being updated, it can be excluded as an error.
- Reduction of required disk space
- The physical row length is 2 bytes shorter per column than when the FIX attribute is not specified. If a table contains many columns, disk space is saved.
(2) Criteria
The FIX attribute should be specified during table definition when all the following conditions are satisfied:
- No columns will be added to the table
- There will be no null values in any column
- No column is variable length
When these conditions are not satisfied, the following should be evaluated:
- Use the 0 (numeric data) or the space (character data) instead of the null value. Note that the null value is treated differently in search conditions and set functions than other values.
- Change variable-length data with a small maximum value or small range of actual lengths to fixed-length data. Note that variable-length data is handled differently in search conditions.
(3) Specification
To assign the FIX attribute to a table, FIX is specified in the CREATE TABLE definition SQL (i.e., CREATE FIX TABLE is specified).