Question

我想从表中选择包含50个最常用列值的所有行。我尝试使用这样的连接，但似乎我选择LEFT JOIN是错误的。声明的内部部分似乎很好。我的陈述中应该改变什么？

SELECT col1, col2 
FROM tbl as t1 
LEFT JOIN (
    SELECT id 
    FROM tbl 
    WHERE id > 123 
      AND id < 987654 
    GROUP BY col1 
    ORDER BY COUNT(id) DESC 
    LIMIT 50
) AS t2 
ON t1.id = t2.id

Answer 1

您是否尝试使用IN运算符作为WHERE子句的一部分而不是JOIN？

例如......

SELECT col1, col2 
FROM tbl as t1 
WHERE t1.id IN (
    SELECT id 
    FROM tbl 
    WHERE id > 123 
        AND id < 987654 
    GROUP BY col1 
    ORDER BY COUNT(id) DESC 
    LIMIT 50
)

Answer 2

如果你的子查询是正确的，右连接应该有效，返回任何匹配的t1到t2的行（而不是t1的所有行和匹配的t2＆＃39; s或null）：

SELECT col1, col2 
FROM tbl as t1 
RIGHT JOIN (
    SELECT id 
    FROM tbl 
    WHERE id > 123 
      AND id < 987654 
    GROUP BY col1 
    ORDER BY COUNT(id) DESC 
    LIMIT 50
) AS t2 
ON t1.id = t2.id

Answer 3

我意识到我的查询没问题，我只想加入col1，而不是id：）

SELECT col1, col2 
FROM tbl as t1 
LEFT JOIN (
  SELECT col1 
  FROM tbl 
  WHERE id > 123 
  AND id < 987654 
  GROUP BY col1 
  ORDER BY COUNT(id) DESC 
  LIMIT 50
) AS t2 
ON t1.col1 = t2.col1

选择具有一列MySQL的最频繁值的行

3 个答案: