SET Operators: UNION, UNION ALL, INTERSECT, MINUS

Referències

• https://www.sqltutorial.org/sql-union/

Teoria

UNION i UNION ALL

SELECT 
    column1, column2
FROM
    table1 
UNION [ALL]
SELECT 
    column3, column4
FROM
    table2;

Per fer la UNION és necessari que les dues selects que vull unir tinguin la mateixa estructura (les mateixes columnes):

SELECT first_name, last_name
FROM employees

UNION

SELECT first_name, last_name
FROM dependents

ORDER BY last_name;

MINUS

Empleats que no tenen dependents:

SELECT employee_id
FROM employees

MINUS 

SELECT employee_id
FROM dependents;

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creat per Joan Quintana Compte, gener 2022