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SQL Basics
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SQL Basics

SQL Basics

1. Selecting
The very first meet with the databaseSELECTing certain columnsLIMITing resultsUnique values from columnUnique values from multiple columnsHow many?How many unique?AliasesTables aliases
2. Filtering
Word filteringNumber filteringCombining conditionsFiltering by numeric intervalMultiple filtering on one columnLIKE filteringNOT like this!
3. Aggregating
MINimal and MAXimal valuesSUMming valuesMean valuesROUNDing
4. Sorting
Sorting by one columnSorting in DESCending orderThe cheapest carSorting by multiple columns
5. Grouping
What is grouping?More aggregate statistics!Grouping by multiple columnsThe cheapest combinationHAVING some conditionsLeast consuming carsFiltering group size
6. Practicing
Challenge: Unique combinationsChallenge: Average Q-series cars priceChallenge: The cheapest new A-series carsChallenge: Relation between engine size and fuel consumptionChallenge: Mileage and manufacture year - is there relation?Challenge: Average price for each model and yearChallenge: The most expensive transmission + engine size combinations

Combining conditions

Often it's not enough to check for only one condition. What if we want to check if multiple conditions hold at the same time? Or at least one of them?

Conditions in SQL can be combined by using AND and OR statements within WHERE block. AND checks if all the conditions hold while OR checks if at least one of the conditions holds. For example, we can combine conditions from the two previous chapters: filter for hybrid cars with mileage less than 5000 miles.


              
123

            
SELECT *
FROM audi_cars
WHERE fueltype = 'Hybrid' AND mileage < 5000
copy

Also, we can extract only either cars with Automatic transmission either with an engine size less than 3 by using OR statement.


              
123

            
SELECT *
FROM audi_cars
WHERE transmission = 'Automatic' OR enginesize < 3
copy

Task

From audi_cars table extract only Diesel cars (fueltype column) with mileage less than 2000.

Task

From audi_cars table extract only Diesel cars (fueltype column) with mileage less than 2000.

Switch to desktop for real-world practiceContinue from where you are using one of the options below

Everything was clear?

Section 2. Chapter 3
toggle bottom row

Combining conditions

Often it's not enough to check for only one condition. What if we want to check if multiple conditions hold at the same time? Or at least one of them?

Conditions in SQL can be combined by using AND and OR statements within WHERE block. AND checks if all the conditions hold while OR checks if at least one of the conditions holds. For example, we can combine conditions from the two previous chapters: filter for hybrid cars with mileage less than 5000 miles.


              
123

            
SELECT *
FROM audi_cars
WHERE fueltype = 'Hybrid' AND mileage < 5000
copy

Also, we can extract only either cars with Automatic transmission either with an engine size less than 3 by using OR statement.


              
123

            
SELECT *
FROM audi_cars
WHERE transmission = 'Automatic' OR enginesize < 3
copy

Task

From audi_cars table extract only Diesel cars (fueltype column) with mileage less than 2000.

Task

From audi_cars table extract only Diesel cars (fueltype column) with mileage less than 2000.

Switch to desktop for real-world practiceContinue from where you are using one of the options below

Everything was clear?

Section 2. Chapter 3
toggle bottom row

Combining conditions

Often it's not enough to check for only one condition. What if we want to check if multiple conditions hold at the same time? Or at least one of them?

Conditions in SQL can be combined by using AND and OR statements within WHERE block. AND checks if all the conditions hold while OR checks if at least one of the conditions holds. For example, we can combine conditions from the two previous chapters: filter for hybrid cars with mileage less than 5000 miles.


              
123

            
SELECT *
FROM audi_cars
WHERE fueltype = 'Hybrid' AND mileage < 5000
copy

Also, we can extract only either cars with Automatic transmission either with an engine size less than 3 by using OR statement.


              
123

            
SELECT *
FROM audi_cars
WHERE transmission = 'Automatic' OR enginesize < 3
copy

Task

From audi_cars table extract only Diesel cars (fueltype column) with mileage less than 2000.

Task

From audi_cars table extract only Diesel cars (fueltype column) with mileage less than 2000.

Switch to desktop for real-world practiceContinue from where you are using one of the options below

Everything was clear?

Often it's not enough to check for only one condition. What if we want to check if multiple conditions hold at the same time? Or at least one of them?

Conditions in SQL can be combined by using AND and OR statements within WHERE block. AND checks if all the conditions hold while OR checks if at least one of the conditions holds. For example, we can combine conditions from the two previous chapters: filter for hybrid cars with mileage less than 5000 miles.


              
123

            
SELECT *
FROM audi_cars
WHERE fueltype = 'Hybrid' AND mileage < 5000
copy

Also, we can extract only either cars with Automatic transmission either with an engine size less than 3 by using OR statement.


              
123

            
SELECT *
FROM audi_cars
WHERE transmission = 'Automatic' OR enginesize < 3
copy

Task

From audi_cars table extract only Diesel cars (fueltype column) with mileage less than 2000.

Switch to desktop for real-world practiceContinue from where you are using one of the options below
Section 2. Chapter 3
Switch to desktop for real-world practiceContinue from where you are using one of the options below
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