Sqlite 使用union时出现SQL语法错误或缺少数据库（靠近“（”：语法错误）

我试图使用union，但我得到了这个模糊的语法错误。我可以让每个查询单独运行，但当我尝试使用union时，我得到了这个错误

(SELECT s.sname, COUNT(s.sname) AS number
FROM sailor s, boat b
WHERE  b.rating <= s.rating
GROUP BY s.sname)
UNION
(SELECT s.sname, 0 AS number
FROM sailor s
WHERE NOT EXISTS(
              SELECT * FROM boat b
              WHERE s.rating >= b.rating));

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在SQL中，只有子查询使用括号。在复合查询中，必须在不使用括号的情况下编写单个选择：

SELECT s.sname, COUNT(s.sname) AS number
FROM sailor s, boat b
WHERE  b.rating <= s.rating
GROUP BY s.sname
UNION
SELECT s.sname, 0 AS number
FROM sailor s
WHERE NOT EXISTS(
              SELECT * FROM boat b
              WHERE s.rating >= b.rating);

在这种特定情况下，您可能只想使用：

SELECT s.sname,
       IFNULL(COUNT(b.rating), 0) AS number
FROM sailor AS s
LEFT JOIN boat AS b
ON b.rating <= s.rating;