使用 group by 子句

Question

查询：

  SELECT sd.ident,sd.suniq, testc, subtestc, ts.testscore, 
         metadept, ts.takendt, 
         MAX(takendt) testdate
    FROM studemo sd, stutests ts, testdef td, udefstu ud
   WHERE ts.suniq =sd.suniq
     AND td.testuniq = ts.testuniq
     AND ts.suniq = ud.suniq
     AND td.testuniq IN ('2000089', '2000090', '2000091', '2000092')
GROUP BY sd.suniq
ORDER BY suniq

得到以下错误：

消息 8120，第 16 级，状态 1，第 2 行 列“studemo.ident”在 选择列表，因为它不是 包含在任一聚合中 函数或 GROUP BY 子句。

我的目标是获得最新的考试成绩。在我尝试添加更多表格以包含更多学生信息之前，我是成功的。

Answer 1

您需要将那些不在聚合函数中的列添加到您的GROUP BY 中，以使您的 SQL 语句有效。

GROUP BY sd.ident,sd.suniq, testc, subtestc, ts.testscore, metadept, ts.takendt

Answer 2

您需要将不使用聚合函数的剩余字段添加到您的Group By。

    select sd.ident,sd.suniq, testc, subtestc, ts.testscore, metadept, ts.takendt, max(takendt)testdate
from studemo sd, stutests ts, testdef td, udefstu ud
where ts.suniq =sd.suniq
and td.testuniq = ts.testuniq
and ts.suniq = ud.suniq
and td.testuniq IN ('2000089', '2000090', '2000091', '2000092')
group by sd.suniq, sd.ident, testc, subtestc, ts.testscore, metadept, ts.takendt
order by suniq

Answer 3

select sd.ident,sd.suniq, testc, subtestc, ts.testscore, metadept, ts.takendt, max(takendt)testdate
from studemo sd, stutests ts, testdef td, udefstu ud
where ts.suniq =sd.suniq
and td.testuniq = ts.testuniq
and ts.suniq = ud.suniq
and td.testuniq IN ('2000089', '2000090', '2000091', '2000092')
group by sd.ident,sd.suniq, testc, subtestc, ts.testscore, metadept, ts.takendt
order by suniq

评论：上面的代码就是@Neil的意思

Answer 4

我怀疑您想显示每个学生的 maxtakedt，即使他们已经参加了多项测试，例如如果他们参加了两次测试，那么您要显示两个测试日期，并在每一行中显示最大日期。如果是这种情况，那么按所有其他列分组将无济于事。也许试试这个，假设 SQL Server 2005 或更高版本：

        WITH md AS
        (
            SELECT ts.suniq, maxdate = MAX(ts.takendt)
                FROM dbo.stutests AS ts
            INNER JOIN
                dbo.testdef AS td
                ON td.testuniq = ts.testuniq
            WHERE
                td.testuniq IN ('2000089', '2000090', '2000091', '2000092')
            GROUP BY ts.suniq
        )
        SELECT
            sd.ident,
            sd.suniq,
            testc, -- which table does this come from? why no prefix?
            subtestc, -- which table does this come from? why no prefix?
            ts.testscore,
            metadept, -- which table does this come from? why no prefix?
            ts.takendt,
            md.maxdate
        FROM
            dbo.studemo AS sd
        INNER JOIN
            dbo.stutests AS ts
            ON sd.suniq = ts.suniq
        INNER JOIN
            dbo.testdef AS td
            ON td.testuniq = ts.testuniq
        INNER JOIN
            dbo.udefstu AS ud
            ON ts.suniq = ud.suniq
        INNER JOIN md
            ON md.suniq = sd.suniq
        WHERE
            td.testuniq IN ('2000089', '2000090', '2000091', '2000092')
        ORDER BY
            sd.suniq; -- you forgot a prefix here too
            -- could cause problems if you change the query later