Question

存储所有时间记录的钓鱼数据库。但是，当有人有联合记录时，我想恢复到第一次捕获作为真实记录。

select * 
from T 
inner join (select Type, 
                   Name, 
                   max(TotDrams) as maxdrams 
            from T 
            WHERE Type='Common Bream' 
            group by Type, Name 
           ) sq on T.Type = sq.Type 
                and T.Name = sq.Name 
                and sq.maxdrams = T.TotDrams 
ORDER BY Ranking ASC

以上内容返回每个名称具有最佳捕获的所有时间记录，但是当记录是联合时，它自然会返回附加记录。我只希望将最早的日期记录包含在所有时间记录中。

有没有办法调整上面的代码来删除额外的联合记录，只挑选最早的记录？

Fishname     Rank            Weight           Angler            Date

Slimey       Rank 1        2 lb   3 oz      John Budd         30/11/2013
Fishy        Rank 2        1 lb   15 oz     Chris Clot        12/01/2009
Scales       Rank 3        1 lb   12 oz     John Budd         21/03/2014
Scales       Rank 3        1 lb   12 oz     Harry White       01/04/2002

通过上面的例子 - 这是目前正在发生的事情，我想删除John Budd的联合记录，因为它是联合的而不是原始的。

另一个注意事项： - 这个SQL将与php一起使用。

Answer 1

您可以在每条鱼捕获的最早日期添加另一个连接。类似的东西：

select * 
from T 
inner join (select Species, 
                   FishName, 
                   max(TotalDrams) as maxdrams 
            from T 
            WHERE Species='Common Bream' 
            AND DateCaught <> ''
            group by Species, FishName 
           ) sq on T.Species = sq.Species 
                and T.FishName = sq.FishName 
                and sq.maxdrams = T.TotalDrams 
inner join (select Species, 
                   FishName, 
                   min(DateCaught) as minDate 
            from T 
            WHERE Species='Common Bream' 
            AND DateCaught <> ''
            group by Species, FishName 
           ) sq2 on T.Species = sq2.Species 
                and T.FishName = sq2.FishName 
                and sq2.minDate = T.DateCaught 
where T.DateCaught <> ''
ORDER BY Rank ASC

接下来，您可以将2个标准重构为单个联接：

select * 
from T 
inner join (select Species, 
                   FishName, 
                   max(TotalDrams) as maxdrams,
                   min(DateCaught) as minDate 
            from T 
            WHERE Species='Common Bream' 
            AND DateCaught <> ''
            group by Species, FishName 
           ) sq on T.Species = sq.Species 
                and T.FishName = sq.FishName 
                and sq.maxdrams = T.TotalDrams 
                and sq.minDate = T.DateCaught 
where T.DateCaught <> ''
ORDER BY Rank ASC

编辑：

对数据结构的进一步分析表明，上面的答案并不完全正确 - 由于日期是varchar，它过滤掉了几条记录，而且对数据结构的假设也不正确。修改后的答案如下：

select distinct 
   T.species,
   t.fishname,
   t.rank,
   t.pounds,
   t.ounces,
   t.drams,
   t.totaldrams,
   t.peg,
   t.angler,
   sq.*,
   sq2.*
FROM (select Species, 
             FishName, 
              max(TotalDrams) as maxdrams
      from T 
      WHERE Species='Common Bream' 
      group by Species, FishName 
     ) sq 
inner join (select Species, 
                   FishName, 
                   TotalDrams,
                   min(if(DateCaught='',STR_TO_DATE('31/12/3099','%d/%m/%Y'),STR_TO_DATE(DateCaught,'%d/%m/%Y'))) as minDate 
            from T 
            WHERE Species='Common Bream' 
            group by Species, FishName, TotalDrams 
           ) sq2 on sq.Species = sq2.Species 
                 and sq.FishName = sq2.FishName 
                 and sq.MaxDrams = sq2.TotalDrams
inner join T on sq.species = T.species 
and sq.fishname = T.fishname
and sq.maxdrams = T.totaldrams
and sq2.mindate = if(DateCaught='',STR_TO_DATE('31/12/3099','%d/%m/%Y'),STR_TO_DATE(DateCaught,'%d/%m/%Y'))

Answer 2

排名后按日期排序，然后按鱼名分组。看起来有用吗？

select * from T inner join (select Species, FishName, max(TotalDrams) as maxdrams from T WHERE Species='Common Bream' group by Species, FishName ) sq on T.Species = sq.Species and T.FishName = sq.FishName and sq.maxdrams = T.TotalDrams GROUP BY T.FishName ORDER BY Rank, DateCaught ASC

Answer 3

我接近这个的方式略有不同，而不是试图将结果限制到最大值，我会排除不是的结果。所以使用类似的东西：

SELECT  T.*
FROM    T
        LEFT JOIN T AS T2
            ON T2.Species = T.Species
            AND T2.FishName = T.FishName
            AND (T2.TotalDrams < T.TotalDrams
                OR (T.TotalDrams = T2.TotalDrams AND T2.DateCaught > T.DateCaught))
WHERE   T.Species = 'Common Bream'
AND     T2.Species IS NULL
ORDER BY T.Rank ASC;

这使用标准的LEFT JOIN/IS NULL方法来排除相同鱼类类型的记录，并且：

TotalDrams

或

TotalDrams 和后来的DateCaught
具有相同的值

<强> Example on SQL Fiddle

由于MySQL实现子查询的方式，您可能会发现这比没有提供所需结果的原始查询表现更好！

修改

好的，新方法。我认为最好的解决方法是使用变量为每条记录存储一个新的行号，然后你可以过滤顶部1.以下将根据订购标准分配你的行号：

SELECT @r:= CASE WHEN @f = t.FishName AND @s:= t.Species THEN @r + 1 ELSE 1 END AS RowNum, @f:= t.FishName AS FishName, @s:= t.Species AS Species, t.Rank, t.Pounds, t.Ounces, t.Drams, t.TotalDrams, t.Peg, t.Angler, STR_TO_DATE(IF(t.DateCaught = '', '31/12/2050', t.DateCaught), '%d/%m/%Y') AS DateCaught FROM T CROSS JOIN (SELECT @f:= '',@s:='', @r:= 0) AS v ORDER BY t.FishName, t.Species, t.TotalDrams DESC, DateCaught ASC;

然后你可以把它放到子查询中，并将记录限制在前1：

SELECT * FROM ( SELECT @r:= CASE WHEN @f = t.FishName AND @s = t.Species THEN @r + 1 ELSE 1 END AS RowNum, @f:= t.FishName AS FishName, @s:= t.Species AS Species, t.Rank, t.Pounds, t.Ounces, t.Drams, t.TotalDrams, t.Peg, t.Angler, t.DateCaught FROM T CROSS JOIN (SELECT @f:= '',@s:='', @r:= 0) AS v ORDER BY t.FishName, t.Species, t.TotalDrams DESC, STR_TO_DATE(IF(t.DateCaught = '', '31/12/2050', t.DateCaught), '%d/%m/%Y') ASC ) AS t WHERE t.RowNum = 1 ORDER BY t.Rank ASC;

<强> Example on SQL Fiddle

这是最灵活的方法，如果您想添加更多规则，即如果您有两个相同的权重，并且在同一日期，您可以为子查询添加进一步的排序，例如Angler。这保证了（鱼名，物种）每个元组只有一个记录，并且给定足够的排序确定性结果。

SQL从“所有时间记录”返回第一个记录日期

3 个答案: