Question

我有一个表和许多数据，如重复值和单个值。但我想只得到重复的值数据，而不是单个值。

Answer 1

SELECT columnWithDuplicates, count(*) FROM myTable
GROUP BY columnWithDuplicates HAVING (count(*) > 1);

Answer 2

上述查询将显示重复的值。一旦你向业务用户提供，他们的下一个问题将是怎么回事？这些是怎么到达那里的？是否有重复的模式？通常更具信息性的是查看包含这些值的整行，以帮助确定为什么存在重复项。

-- this query finds all the values in T that
-- exist in the derived table D where D is the list of
-- all the values in columnWithDuplicates that occur more than once
SELECT DISTINCT
    T.* 
FROM
    myTable T 
    INNER JOIN 
    (
        -- this identifies the duplicated values
        -- courtesy of Brian Roach
        SELECT 
            columnWithDuplicates
        ,   count(*) AS rowCount
        FROM 
            myTable 
        GROUP BY 
            columnWithDuplicates 
        HAVING 
            (count(*) > 1)
    ) D 
        ON D.columnWithDuplicates = T.columnWithDuplicates

如何从一个表中仅获取重复数据？

2 个答案: