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Constraints and Load
Operations
How database contents get changed
Data integrity tools
Constraints
See "Creating tables" for more information on how constraints affect
optimization. For more on join indexes and foreign keys, see "Using join
indexes".
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.
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
•
A new row may be inserted into a table, using the
To assist in maintaining data integrity, you can use data constraints, and
constraints that specify the referential structure of the database.
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
entry is later than a
date_returned
CHAPTER 7
Ensuring Data Integrity
DELETE
INSERT
entry.
date_borrowed
statement.
statement.
275
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