sql：如果两行有重复的id，则只保留最小值

Question

以下是我的示例数据。第3行和第4行具有相同的st_case（主键），但它们的dist_min不同。我想保持行具有最小dist_min值。请注意，可能有超过2个重复行与同一个st_case关联。非常感谢你的帮助！

Answer 1

在MySQL中，您可以使用delete和join：

执行此操作

delete s
    from sample s left join
         (select st_case, min(dist_min) as mindm
          from sample s
          group by st_case
         ) ss
         on ss.st_case = s.st_case and s.dist_min > ss.mindm;

Answer 2

你可以尝试这个：

DELETE t1 FROM table AS t1
LEFT JOIN table t2 ON t1.st_case = t2.st_case 
WHERE t1.dist_min > t2.dist_min

Answer 3

DELETE FROM sample 
WHERE dist_min !=(SELECT dist_min FROM (SELECT * FROM sample) sample2 
                  WHERE sample2.st_case = sample.st_case 
                  ORDER BY dist_min 
                  LIMIT 1)

Answer 4

正如SAM M建议的那样，我不确定如何让具有相同主键的重复行。 但是，如果st_case不是您唯一的密钥，并且该表具有复合密钥 或者它是一个非关键专栏， 您可以编写一个触发器来控制插入 类似的东西：

CREATE table CALC_STATUS(id varchar(40), correlatoinToken integer, requirement double)

CREATE TRIGGER keep_min BEFORE INSERT ON CALC_STATUS 
    FOR EACH row 
BEGIN 
    IF NEW.correlatoinToken = correlatoinToken AND NEW.requirement <= requirement then
    SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = "A row with similar correlation token with lower requirement already exists";
ELSEIF NEW.correlatoinToken = correlatoinToken AND NEW.requirement > requirement
    NEW.requirement = requirement;
END IF;
END;

如果您打算查询：

SELECT c1.* FROM CALC_STATUS c1,(SELECT st_case,MIN(dist_min) FROM CALC_STATUS GROUP BY road_id) AS c2 WHERE c1.st_case=c2.st_case

Answer 5

我没有测试这个，所以请原谅任何语法错误。 SQL ranking functions可以解决您的问题。基本上，您按一列分组，然后按另一列排名。然后你只能选择一级的那些。

SELECT * 
FROM(
  SELECT *, Rank() OVER (PARTITION BY 'st_case' Order by Dist_min DESC) as Rank
  From 'tbl_Name')
WHERE Rank = '1'