How interrogate these work?

Hello gurus.

I have a doubt for these two queries

I list the names of employees and their commissions and excludes the name of the employee who has no commissions.

select last_name,nvl(commission_pct,0) from employees where commission_pct <>  null;

The output of the query is selected lines

select last_name,nvl(commission_pct,0) from employees where commission_pct is not null;

The output of the above query indicating the name of the employee and the commission, whose values are not null

Is 'not null' and ' <>' null are the same?

When you use different or equal to (=) of (! =, <> ) operator with NULL always returns false. You should always use IS NULL or IS NOT NULL when checking if a column value is null or not null.

Here's a simple example.

SQL > create table a (cervical integer);

Table created.

SQL > insert into a values (null);

1 line of creation.

SQL > select * from where a col = null;

no selected line

SQL > insert into a values (1);

1 line of creation.

SQL > select * from where a col <> null;

no selected line

SQL > select * from where a col has the value null.

COL
----------

SQL > select * from where a col is not null;

COL
----------
1

Tags: Database

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