SQL - SELECT - FOREIGN KEY

Question

VISITSEXIT              VISITSENTRY               VISITOR
idvisitsexit            idvisitsentry             idvisitor 
idvisitsentry           idvisitante               visitor 
idvisitor               visitor
visitor
dateexit
timeexit

我需要选择表VISITSEXIT，当她带来VISITSENTRY时，也会带来idvisitor和访问者（访客）的描述。

Answer 1

一个简单直截了当的JOIN会给你你想要的东西：

SELECT
  t.idvisitor,
  t.visitor,
  t.dateexit,
  t.timeext,
  ... -- the rest of the columns you want to select 
FROM VISITSEXIT       AS t
INNER JOIN VisitEntry AS e ON t.idvisitentry = e.visitentry
INNER JOIN Visitor    AS v ON e.idvisitante  = v.idvisitor;

如果要包含其他表中不匹配的行，则可能还需要使用LEFT JOIN。有关JOIN类型的详细信息，请参阅此帖子：

• A Visual Explanation of SQL Joins