Database Reference
In-Depth Information
3.
Most DBMS suites provide a utility that allows the user to key
data into the table, once it has been created. Earlier versions
of Oracle do not. However, through Enterprise Manager, later
versions (starting with Oracle 9i) do.
4.
Data can be entered in the table via the SQL insert statement
(which you will learn in Chapter 12) or an application
program, written for that purpose.
5.
The matter of missing values is of much concern to any
creditable DBMS. In DB2 and Oracle, nulls are used to
represent missing or irrelevant information. Note that null
is not the same as zero or blank. If nulls are allowed for an
attribute and no data is provided, the system provides a null
value for that attribute.
6.
In many modern DBMS, a GUI sits on top of SQL definition
statements so user may not use them.
7.
Some DBMS, (e.g. Oracle) provide the user with the flexibility
of specifying which attribute of a referenced table is to be used
in the foreign key characteristic.
8.
The operator specified in the Check-Clause may be any valid
Boolean operator as defined in Chapters 7 and 8. When the
third form of the Check-Clause is used, the column specified
must be one of the values specified.
9.
Value, Value1 and Value2 in the Check-Clause represent
literal values.
Example 1: To create base relations Program , Course and Pgm-Struct as described
in Chapter 7.
Search WWH ::




Custom Search