Запросы к базе данных

Средний уровень SQL

Jasmin Ludolf

Data Science Content Developer, DataCamp

Структура курса

Логотип PostgreSQL

Схема базы данных films с четырьмя таблицами, именами полей и типами данных

SELECT COUNT(birthdate) AS count_birthdates
FROM people;

|count_birthdates|
|----------------|
|6152            |

SELECT COUNT(name) AS count_names, COUNT(birthdate) AS count_birthdates
FROM people;

|count_names|count_birthdates|
|-----------|----------------|
|6397       |6152            |

SELECT COUNT(*) AS total_records
FROM people;

|total_records|
|-------------|
|8397         |

SELECT language
FROM films;

|language |
|---------|
|Danish   |
|Danish   |
|Greek    |
|Greek    |
|Greek    |

SELECT DISTINCT language
FROM films;

|language |
|---------|
|Danish   |
|Greek    |

SELECT COUNT(DISTINCT birthdate) AS count_distinct_birthdates
FROM people;

|count_distinct_birthdates|
|-------------------------|
|5398                     |

Средний уровень SQL