Returning all data from a table
Select some columns
Filtering rows
Logic
Text patterns
To be or NULL to be
A bit of mathematics
Let's practice
Instruction
In every row, there can be NULL values – unknown missing values. Remember the Opel from our table with its missing price? That missing price is represented with a NULL value.
To check whether a column has a value, we use a special instruction IS NOT NULL.
SELECT Id FROM User WHERE MiddleName IS NOT NULL;
This code selects only those users who have a middle name (i.e., that user's MiddleName column has a known value).
Exercise
Select all cars that have a price.
Stuck? Here's a hint!
Type:
SELECT * FROM Car WHERE Price IS NOT NULL;
