Where Statements

• Where statements ignore Null Values, as it treats it as unknown
• Say I have this table Customers….

ID	Name	Age	Email
1	Alice	30	[email protected]
2	Bob	null	[email protected]
3	Charlie	25	null
4	Dave	45	[email protected]
5	Eve	null	null

Say I want Customers whose age is not 30

SELECT Name 
FROM Customers 
WHERE Name != 30

This will only return Charlie and Dave, but maybe we want Bob and Eve too. Then in this case, we need to include Or Name is Null

SQL Distinct Keyword

• for a Set, it returns the distinct combinations of a column (or a set of columns)

NOT Keyword

• Put NOT in front of a logical operator to return the opposite. E.g the bottom will return TRUE

NOT LENGTH('hi') > 15

Left JOIN

• Joins join two tables together column wise. A reminder that all joins need the on keyword
• Say we have two tables
• If we have table A and left join table B onto it, matching records on table B will be returned