Sommario
Quanti tipi di join ci sono in access?
Esistono quattro tipi di join fondamentali: inner join, outer join, cross join e unequal join.
Quando usare left e right join?
LEFT JOIN: estrae tutti i valori della tabella a sinistra anche se non hanno corrispondenza nella tabella a destra; RIGHT JOIN: estrae tutti i valori della tabella a destra anche se non hanno corrispondenza nella tabella di sinistra.
Come funziona LEFT join?
Il qualificatore Left Join include tutte le righe della prima tabella (Persone). A questa tabella aggiunge le colonne della seconda tabella (Paternità) quando le colonne Nome = Figlio hanno lo stesso valore. In questo modo visualizzo l’informazione del padre di ogni persona.
Cosa fa il LEFT join?
What is the difference between inner and outer join?
An Inner Join returns only the rows that have matching values in both the tables (we are considering here the join is done between the two tables). What is Outer Join?
What does a RIGHT OUTER JOIN look like?
Now, here is what the result of running this SQL would look like: Right Outer Join:- A right outer join (or right join) closely resembles a left outer join, except with the treatment of the tables reversed. Every row from the “right” table (Location) will appear in the joined table at least once.
What does a LEFT OUTER JOIN return?
A left outer join will return all the data in Table 1 and all the shared data (so, the inner part of the Venn diagram example), but only corresponding data from Table 2, which is the right join.
What is a FULL OUTER JOIN in SQL?
FULL OUTER JOIN As the name indicates, full outer join returns all data from both database tables, and it looks like we are using both Left and Right outer joins at the same time. In the case of our example, both tables were not the same length tables, so you can find two nulls which are for Broccoli and Tomatoes, in the result table.