如何识别SQL中的重复值

Question

我正在尝试查找特定数据集中生成的重复项

我原来的查询是

SELECT 
    b.admidate, a.token_person_id,
    COUNT (DISTINCT(a.token_person_id)) AS patientCount
FROM 
    new_alzheimers_agegroup2 a
LEFT JOIN
    inpatient_mapping b ON b.token_person_id = a.token_person_id 
                        AND a.indexdate = b.disdate
ORDER BY 
    a.token_person_id

但与原始数据相比，我发现有 1500 个重复项。如何构建可以查找重复项的查询？

Answer 1

要识别数据集中的重复项，您可以编写一个查询，按您怀疑导致重复项的列进行分组，然后对出现次数进行计数。如果出现次数大于 1，则有重复项。

SELECT 
    b.admidate, 
    a.token_person_id,
    COUNT(*) AS occurrenceCount
FROM 
    new_alzheimers_agegroup2 a
LEFT JOIN
    inpatient_mapping b ON b.token_person_id = a.token_person_id 
                        AND a.indexdate = b.disdate
GROUP BY 
    b.admidate, 
    a.token_person_id
HAVING 
    COUNT(*) > 1
ORDER BY 
    occurrenceCount DESC;