diferencia entre la unión externa y la unión interna SQL
In SQL, a join is used to compare and combine — literally join — and
return specific rows of data from two or more tables in a database.
An inner join finds and returns matching data from tables,
while an outer join finds and returns matching data and some dissimilar
data from tables
INNER JOIN :
The inner join will keep only the information from the two joined tables
that is related.
OUTER JOIN:
There are three types of outer joins:
Left Outer Join (or Left Join)
Right Outer Join (or Right Join)
Full Outer Join (or Full Join)
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