Question

我无法弄清楚我的SQL查询出了什么问题

我的查询

SELECT distinct tp.class, tp.country 
FROM classes as tp, (SELECT distinct battle 
                     FROM outcomes 
                     WHERE outcomes.ship in (SELECT ships.name 
                                             FROM ships 
                                             WHERE ships.class = tp.class)) as sq 
GROUP BY tp.class, tp.country;

出现错误

ERROR:  invalid reference to FROM-clause entry for table "tp"  

LINE 1: ...(select ships.name from ships where ships.class = tp.class))...
                                                             ^
HINT:  There is an entry for table "tp", but it cannot be referenced from this part of the query.

我正在使用PostgreSQL12。
我在堆栈溢出时看到了其他类似的问题，但是我无法从给定的解决方案中找出错误。

Answer 1

您可以只使用一个简单的join

SELECT distinct tp.class, tp.country 
FROM classes as tp join ships on ships.class = tp.class
join outcomes on outcomes.ship=ships.name

Answer 2

您在from子句中有一个相关子查询。这是允许的，但是您需要横向连接：

SELECT DISTINCT tp.class, tp.country 
FROM classes tp CROSS JOIN LATERAL
     (SELECT DISTINCT o.battle 
      FROM outcomes o
      WHERE o.ship IN (SELECT s.name 
                       FROM ships s
                       WHERE s.class = tp.class
                      )
     ) as sq ;

也许还有其他写查询的方法，但这似乎是您在此处尝试的方法。

错误：对表“ tp”的FROM子句条目的引用无效

2 个答案: