如果只从t3中选择了一行，则：

SELECT t3.rc, t2.rcs
FROM   t2
       INNER JOIN t3
       ON t3.rc LIKE t2.rcs || '%'
ORDER BY LENGTH(t2.rcs) DESC
FETCH FIRST ROW ONLY

如果t3中有多行，并且希望每行都有最佳匹配，则：

SELECT t3.rc,
       t2.rcs
FROM   t3
       CROSS JOIN LATERAL (
         SELECT rcs
         FROM   t2
         WHERE  t3.rc LIKE t2.rcs || '%'
         ORDER BY LENGTH(t2.rcs) DESC
         FETCH FIRST ROW ONLY
       ) t2

或：

SELECT rc,
       rcs
FROM   (
  SELECT t3.rc,
         t2.rcs,
         ROW_NUMBER() OVER (PARTITION BY t3.rc ORDER BY LENGTH(t2.rcs) DESC) AS rn
  FROM   t2
         INNER JOIN t3
         ON t3.rc LIKE t2.rcs || '%'
)
WHERE  rn = 1;

对于您的示例数据，所有输出：
| RC|雷达散射截面|
| - ------|- ------|
| 小行星441|四四一|
fiddle