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SQL Basics

See the whole table
Select some columns
Filtering rows
Logic
Text patterns
To be or NULL to be
20. Comparisons with NULL
A little bit of mathematics
Let's practice

Instruction

Good job. Remember, NULL is a special value. It means that some piece of information is missing or unknown.

If you set a condition on a particular column, say AGE < 70, the rows where age is NULL will always be excluded from the results. Let's check that in practice.

In no way does NULL equal zero. What's more, the expression NULL = NULL is never true in SQL!

Exercise

Select all columns for cars whose price column is greater than or equal to zero.

Note that the Opel with an unknown price is not in the result.

Stuck? Here's a hint!

Type:

SELECT *
FROM car
WHERE price >= 0;