postgresql - PostgreSQL 的这两个查询有什么区别？

Question

这 2 个查询在相同的条件下获取相同的列。但结果仍然不同:

首先使用连接:

select 
  s.codice as codice,
  n.ragione_sociale as ragione_sociale  
from 
  parco_veicoli pv
right join 
  noleggiatori n on pv.id_noleggiatore = n.id
right join 
  sedi s on pv.id_sede = s.id  
  order by codice, ragione_sociale;

第一个查询给出总共 1323 行的输出。

没有连接的第二个:

SELECT 
  s.codice as codice,
  n.ragione_sociale as ragione_sociale
FROM 
  parco_veicoli pv,  
  noleggiatori n, 
  sedi s
WHERE 
  pv.id_sede = s.id AND
  pv.id_noleggiatore = n.id 
  order by codice, ragione_sociale;

第二个查询给出总共 1321 行的输出。

问题:

谁能告诉我这两个查询的含义相同还是不同？

因为输出几乎相同，但第二个查询的结果集(行)比第一个查询少。

Answer 1

https://www.postgresql.org/docs/current/static/queries-table-expressions.html

FROM T1 CROSS JOIN T2 is equivalent to FROM T1 INNER JOIN T2 ON TRUE (see below). It is also equivalent to FROM T1, T2.

和

RIGHT OUTER JOIN

First, an inner join is performed. Then, for each row in T2 that does not satisfy the join condition with any row in T1, a joined row is added with null values in columns of T1. This is the converse of a left join: the result table will always have a row for each row in T2.

所以在您的查询中，第二个是 INNER join，第一个是 RIGHT OUTER JOIN