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Using Pragma RESTRICT_REFERENCES:
The function called from the SQL statements should obey certain rules meant to control the side effects. To check for violation of the rules, you can use the RESTRICT_REFERENCES pragma that instructs the compiler to report reads and/or writes to database tables and/or package variables.
Avoiding Deadlocks
In some situations when executing a SQL data definition statement, the outcome is a deadlock.
For illustration, the procedure below causes a deadlock as it attempts to drop itself. To avoid the deadlocks, never try to ALTER or DROP a subprogram or package while you are still using it.
CREATE PROCEDURE calc_bonus (emp_id NUMBER) AS
BEGIN
...
EXECUTE IMMEDIATE 'DROP PROCEDURE calc_bonus';
-- causes "timeout occur while waiting to the lock object" error
END;
SQL Operators The PL/SQL uses all the SQL set, comparison, and row operators in the SQL statements. This part briefly describes some of these operators. 1. Comparison Opera
Using DELETE This process has three forms. The DELETE removes all elements from the collection. DELETE(n) removes the nth element from the nested table. When n is null, then D
Example of Null operator - NiNo Rule If we wanted to make HIGHER_OF adhere to "NULL in, NULL out"-let's call it the NiNo rule-we would have to write something like what is sho
Data Abstraction The Data abstraction extracts the important properties of data while ignoring the not necessary details. Once you design a data structure, you can fail to reme
Effects of NULL The numeric variable X, perhaps of type INTEGER, might be assigned NULL. In that case the result of evaluating X + 1 is NULL, and so SET Y = X + 1 assigns NULL
Use Object Types and Collections The Collection types and object types increase your efficiency by allowing for the realistic data modeling. The Complex real-world entities an
EXECUTE IMMEDIATE Statement The EXECUTE IMMEDIATE statement prepare (parses) and instantly executes a dynamic SQL statement or an anonymous PL/SQL block. Syntax:
Keyword & Parameter Description: PRAGMA: These keywords signify that the statement is a pragma (i.e. compiler directive). The Pragmas are processed at the compile time, n
IN Operator The operator IN tests the set membership. This means "equal to any member of." The set may have nulls, but they are ignored. For illustration, the statement below do
Example of Foreign Key Constraint Example: Alternative formulation for 6.3 as a foreign key constraint ALTER TABLE EXAM_MARK ADD CONSTRAINT Must_be_enrolled_to_take_exam
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