Asumiendo que se está haciendo un join de columnas sin duplicados, lo cuál es un caso común: Un inner join de A y B entregará el resultado de la intersección de los conjuntos A y B. En otras palabras, la parte interna –intersección– en un diagrama de Venn. The fact that when it says INNER JOIN, you can be sure of what it does and that it's supposed to be just that, whereas a plain JOIN will leave you, or someone else, wondering what the standard said about the implementation and was the INNER/OUTER/LEFT left out by accident or by purpose.

Understanding the Context

INNER JOIN gets all records that are common between both tables based on the supplied ON clause. LEFT JOIN gets all records from the LEFT linked and the related record from the right table ,but if you have selected some columns from the RIGHT table, if there is no related records, these columns will contain NULL. RIGHT JOIN is like the above but gets all records in the RIGHT table. FULL JOIN ...

Key Insights

What's the difference between INNER JOIN, LEFT JOIN, RIGHT JOIN and ... Inner join faz uma junção entre duas tabelas A e B onde a projeção serão todos os elementos de A que estão em B. Ex.: Quero todos os clientes de um banco e suas determinadas agencias: select * from Clientes inner join Agencias on Cliente.idAgencia = Agencias.idAgencia Um outer join pode ser Left, Rigth e Center (ou Cross). Um left join faz uma junção entre A e B onde a projeção ... Inner join is a join that combined tables based on matching tuples, whereas outer join is a join that combined table based on both matched and unmatched tuple.

Final Thoughts

Inner join merges matched row from two table in where unmatched row are omitted, whereas outer join merges rows from two tables and unmatched rows fill with null value.