Question

以下查询中的所有内容都会为每个具有正确信息的invBlueprintTypes行生成一行。但我正在尝试添加一些东西。请参见下面的代码块。

Select
  blueprintType.typeID,
  blueprintType.typeName Blueprint,
  productType.typeID,
  productType.typeName Item,
  productType.portionSize,
  blueprintType.basePrice * 0.9 As bpoPrice,
  productGroup.groupName ItemGroup,
  productCategory.categoryName ItemCategory,
  blueprints.productionTime,
  blueprints.techLevel,
  blueprints.researchProductivityTime,
  blueprints.researchMaterialTime,
  blueprints.researchCopyTime,
  blueprints.researchTechTime,
  blueprints.productivityModifier,
  blueprints.materialModifier,
  blueprints.wasteFactor,
  blueprints.maxProductionLimit,
  blueprints.blueprintTypeID
From
  invBlueprintTypes As blueprints
  Inner Join invTypes As blueprintType On blueprints.blueprintTypeID = blueprintType.typeID
  Inner Join invTypes As productType On blueprints.productTypeID = productType.typeID
  Inner Join invGroups As productGroup On productType.groupID = productGroup.groupID
  Inner Join invCategories As productCategory On productGroup.categoryID = productCategory.categoryID
Where
  blueprints.techLevel = 1 And
  blueprintType.published = 1 And
  productType.marketGroupID Is Not Null And
  blueprintType.basePrice > 0

所以我需要在这里得到的是下面的表及其下面的列，因此我可以使用值timestamp并按profitHour对整个结果进行排序

tablename: invBlueprintTypesPrices
columns:   blueprintTypeID, timestamp, profitHour

我需要这些信息，并考虑以下选择。使用select来显示我对JOIN / in-query select的意图或者可以执行此操作的任何内容。

SELECT * FROM invBlueprintTypesPrices 
WHERE blueprintTypeID = blueprintType.typeID 
ORDER BY timestamp DESC LIMIT 1

即使没有来自invBlueprintTypesPrices的结果，我还需要表invBlueprintTypes中的主行仍然显示。 LIMIT 1是因为我想要最新的行，但删除旧数据不是一个选项，因为需要历史记录。

如果我理解正确，我认为我需要一个子查询选择，但如何做到这一点？我已经厌倦了在查询结束后使用AS blueprintPrices添加上面的确切查询，但是没有使用

的错误

WHERE blueprintTypeID = blueprintType.typeID

部分是错误的焦点。我不知道为什么。有谁能解决这个问题？

Answer 1

你没有说你要把子查询放在哪里。如果在select子句中，那么由于返回多个值而出现问题。

你不能直接将它放入from子句，因为你有一个相关的子查询（不允许）。

相反，你可以像这样把它放进去：

from . . .
     (select *
      from invBLueprintTypesPrices ibptp
      where ibtp.timestamp = (select ibptp2.timestamp
                              from invBLueprintTypesPrices ibptp2
                              where ibptp.blueprintTypeId = ibptp2.blueprintTypeId
                              order by timestamp desc
                              limit 1
                             )
     ) ibptp
     on ibptp.blueprintTypeId = blueprintType.TypeID

这标识了子查询中所有blueprintTypeid的最新记录。然后它加入匹配的那个。

Answer 2

您需要使用LEFT JOIN来检查invBlueprintTypesPrices中的NULL值。要模仿每个TypeId LIMIT 1，您可以使用MAX()或者真正确保只返回单个记录，使用行号 - 这取决于您是否可以有多个最大时间戳每种类型的id。假设没有，那么这应该是关闭的：

Select
  ...
From
  invBlueprintTypes As blueprints
  Inner Join invTypes As blueprintType On blueprints.blueprintTypeID = blueprintType.typeID
  Inner Join invTypes As productType On blueprints.productTypeID = productType.typeID
  Inner Join invGroups As productGroup On productType.groupID = productGroup.groupID
  Inner Join invCategories As productCategory On productGroup.categoryID = productCategory.categoryID
  Left Join (
    SELECT MAX(TimeStamp) MaxTime, TypeId
    FROM invBlueprintTypesPrices 
    GROUP BY TypeId
  ) blueprintTypePrice On blueprints.blueprintTypeID = blueprintTypePrice.typeID 
  Left Join invBlueprintTypesPrices blueprintTypePrices On 
    blueprintTypePrice.TypeId = blueprintTypePrices.TypeId AND
    blueprintTypePrice.MaxTime = blueprintTypePrices.TimeStamp 
Where
  blueprints.techLevel = 1 And
  blueprintType.published = 1 And
  productType.marketGroupID Is Not Null And
  blueprintType.basePrice > 0
Order By
  blueprintTypePrices.profitHour

假设您的最大时间戳可能与2个不同的记录相同，请将上面的2个左连接替换为与此类似的内容：

Left Join (
    SELECT @rn:=IF(@prevTypeId=TypeId,@rn+1,1) rn, 
         TimeStamp, 
         TypeId, 
         profitHour, 
         @prevTypeId:=TypeId
    FROM (SELECT * 
          FROM invBlueprintTypesPrices 
          ORDER BY TypeId, TimeStamp DESC) t
       JOIN (SELECT @rn:=0) t2
  ) blueprintTypePrices On blueprints.blueprintTypeID = blueprintTypePrices.typeID AND blueprintTypePrices.rn=1

MySQL内部加入where子句排序和限制，子查询？

2 个答案: