SQL 选择联合后的最大日期

Question

我想从三个联合行记录中选择最上面的日期（基于我的 SQL 查询），但我遇到了这个错误：

选择列表中的列 'tbl1.intDocID' 无效，因为它既不包含在聚合函数中，也不包含在 GROUP BY 子句中。

SELECT TOP 1 
    a.YearX, intClientCode
FROM 
    (SELECT intDocID, MAX(dtY1) AS YearX, 1 AS position 
     FROM [tbl1] WHERE intDocID = '834'
     UNION ALL
     SELECT intDocID, dtY2, 2 FROM [tbl1] 
     WHERE intDocID = '834'
     UNION ALL
     SELECT intDocID, dtY3, 3 FROM [tbl1] 
     WHERE intDocID = '834') a
ORDER BY 
    a.YearX DESC

Answer 1

您需要在您的选择语句中添加 GROUP BY 子句。 GROUP BY 语句需要使用聚合函数（COUNT、MAX、MIN、SUM、AVG）来按一列或多列对结果集进行分组

SELECT TOP 1 
    a.YearX, intClientCode 
FROM
    (SELECT intDocID, MAX(dtY1) AS YearX, 1 AS position FROM [tbl1] 
     WHERE intDocID = '834' 
     GROUP BY intDocID
     UNION ALL
     SELECT intDocID, dtY2, 2 FROM [tbl1] 
     WHERE intDocID = '834' 
     UNION ALL
     SELECT intDocID, dtY3, 3 FROM [tbl1] 
     WHERE intDocID = '834') a

ORDER BY a.YearX desc