SQL check

descrivi cosa fa la seguente query

SELECT

fp.id,

first_name,

last_name,

national_team_id,

country,

games_played

FROM football_players fp

JOIN national_team nt

ON fp.national_team_id = nt.id

ORDER BY fp.id;

descrivi cosa fa la seguente query

SELECT

fp.id,

first_name,

last_name,

national_team_id,

country,

games_played

FROM football_players fp

LEFT JOIN national_team nt

ON fp.national_team_id = nt.id

ORDER BY fp.id;

descrivi cosa fa la seguente query

SELECT

fp.id,

first_name,

last_name,

national_team_id,

country,

games_played

FROM football_players fp

RIGHT JOIN national_team nt

ON fp.national_team_id = nt.id

ORDER BY fp.id;

descrivi cosa fa la seguente query

SELECT

fp1.id,

fp1.first_name,

fp1.last_name,

fp1.national_team_id,

fp2.id AS id_2,

fp2.first_name AS first_name_2,

fp2.last_name AS last_name_2,

fp2.national_team_id as national_team_id_2

FROM football_players fp1

JOIN football_players fp2

ON fp1.id <> fp2.id

AND fp1.national_team_id = fp2.national_team_id;

cosa fa la seguente interrogazione

SELECT

first_name,

last_name,

mobile_data_limit,

data_used,

period

FROM mobile_user mu

JOIN data_usage du

ON mu.id = du.mobile_user_id

AND mobile_data_limit < data_used;

descrivi la seguente query

SELECT DISTINCT loan_duration

FROM loans

ORDER BY loan_duration;

Descrivi la seguente query

SELECT

column_1,

column_2,

…,

FROM table_name

WHERE …

GROUP BY column_1, column_2

HAVING …

ORDER BY column_1, column_2;

descrivi la seguente query

SELECT

department,

AVG(salary) AS average_salary

FROM salaries

GROUP BY department;

descrivi la seguente query

SELECT

department,

AVG(salary) AS average_salary

FROM salaries

GROUP BY department

HAVING AVG(salary) < 5500;

descrivi la seguente query

SELECT

first_name,

last_name,

start_date,

termination_date

FROM contributors

WHERE termination_date != '2022-10-01';