Oracle Learning - 9

Oracle/PLSQL: IS NULL

In other languages, a null value is found using the = null syntax. However in PLSQL to check if a value is null, you must use the "IS NULL" syntax.
To check for equality on a null value, you must use "IS NULL".
For example,
IF Lvalue IS NULL then
.
END IF;
If Lvalue contains a null value, the "IF" expression will evaluate to TRUE.

You can also use "IS NULL" in an SQL statement. For example:
select * from suppliers
where supplier_name IS NULL;
This will return all records from the suppliers table where the supplier_name contains a null value.

Oracle/PLSQL: IS NOT NULL

In other languages, a not null value is found using the != null syntax. However in PLSQL to check if a value is not null, you must use the "IS NOT NULL" syntax.
For example,
IF Lvalue IS NOT NULL then
.
END IF;
If Lvalue does not contain a null value, the "IF" expression will evaluate to TRUE.

You can also use "IS NOT NULL" in an SQL statement. For example:
select * from suppliers
where supplier_name IS NOT NULL;
This will return all records from the suppliers table where the supplier_name does not contain a null value.

Oracle/PLSQL: IF-THEN-ELSE Statement

There are three different syntaxes for these types of statements.
Syntax #1: IF-THEN
IF condition THEN
{...statements...}
END IF;

Syntax #2: IF-THEN-ELSE
IF condition THEN
{...statements...}
ELSE
{...statements...}
END IF;

Syntax #3: IF-THEN-ELSIF
IF condition THEN
{...statements...}
ELSIF condition THEN
{...statements...}
ELSE
{...statements...}
END IF;

Here is an example of a function that uses the IF-THEN-ELSE statement:
CREATE OR REPLACE Function IncomeLevel
( name_in IN varchar2 )
RETURN varchar2
IS
monthly_value number(6);
ILevel varchar2(20);
cursor c1 is
select monthly_income
from employees
where name = name_in;
BEGIN
open c1;
fetch c1 into monthly_value;
close c1;
IF monthly_value <= 4000 THEN ILevel := 'Low Income'; ELSIF monthly_value > 4000 and monthly_value <= 7000 THEN ILevel := 'Avg Income'; ELSIF monthly_value > 7000 and monthly_value <= 15000 THEN
ILevel := 'Moderate Income';
ELSE
ILevel := 'High Income';
END IF;
RETURN ILevel;
END;
In this example, we've created a function called IncomeLevel. It has one parameter called name_in and it returns a varchar2. The function will return the income level based on the employee's name.