SQL Select 联合后的最大日期

Question

我想 select 三个联合行记录中的最高日期（基于我的 SQL 查询），但我遇到了这个错误：

Column 'tbl1.intDocID' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

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 select 语句中添加 GROUP BY 子句。 GROUP BY 语句需要聚合函数（COUNT、MAX、MIN、SUM、AVG）按一个或多个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