Sybase 12.4.2 - Manual (Page 295)

CHAPTER 7 Ensuring Data Integrity
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See “Creating tables” for more information on how constraints affect
optimization. For more on join indexes and foreign keys, see “Using join
indexes”.
Constraints and Load
Operations Adaptive Server IQ checks during load operations that certain constraints are
obeyed:
• Adaptive Server IQ ensures that data being loaded is the appropriate data
type and length.
• If you have a join index that relies on a foreign key-primary key
relationship, when synchronizing the join index Adaptive Server IQ
checks that data in the underlying tables maintains the expected one-to-
many relationship between the joined columns.
How database contents get changed
Information in database tables is changed by submitting SQL statements from
client applications. Only a few SQL statements actually modify the
information in a database.
• An existing row of a table may be deleted, using the DELETE statement.
• A new row may be inserted into a table, using the INSERT statement.
Data integrity tools
To assist in maintaining data integrity, you can use data constraints, and
constraints that specify the referential structure of the database.
Constraints You can use several types of constraints on the data in individual columns or
tables. For example:
• A NOT NULL constraint prevents a column from containing a null entry.
Adaptive Server IQ enforces this constraint.
• Columns can have unenforced CHECK conditions assigned to them, to
specify that a particular condition should be met by every item in the
column. You could specify, for example, that salary column entries should
be within a specified range.
• Unenforced CHECK conditions can be made on the relative values in
different columns, to specify, for example, in a library database that a
date_returned entry is later than a date_borrowed entry.