选择不同表格中的字段

Question

我需要从不同的数据库中选择不同的字段。其中一个字段是从不同表格中选择LastUpdateOn日期时间字段的最大值。

{项目}，{文件}，{指导}，{文件}，{用户}，{ProjectParticipant}是不同的表

SELECT {Project}.[Number],{Project}.[Name],{User}.[Last_Login],{A}.[max_LastUpdatedOn] 

From {Project} 

INNER JOIN {ProjectParticipant} ON {Project}.[Id] = {ProjectParticipant}.[ProjectId] 
INNER JOIN {User} ON {ProjectParticipant}.[UserId] = {User}.[Id] AND {User}.[Username] = @UserId 
INNER JOIN {Document} ON {Project}.[Id] = {Document}.[ProjectId] 
INNER JOIN {InstructionType} ON {Project}.[Id] = {Instruction}.[ProjectId] 
INNER JOIN {Question} ON {Project}.[Id] = {Question}.[ProjectId] 

SELECT MAX(LastUpdatedOn) AS max_LastUpdatedOn 
FROM 
(
    SELECT LastUpdatedOn FROM {Question} 
    UNION ALL 
    SELECT LastUpdatedOn FROM {Document} 
    UNION ALL 
    SELECT LastUpdatedOn FROM {Instruction} 
) A; 

GROUP BY {Project}.[Number], 
     {Project}.[Name], 
     {User}.[Last_Login] 
     {A}.[max_LastUpdatedOn] 
ORDER BY {Project}.[Number] 

但得到一个错误说{A}是一个未知的实体。我不确定这里有什么问题。 使用

SELECT {Project}.[Number],{Project}.[Name],{User}.[Last_Login], 
(SELECT MAX(LastUpdatedOn) as max_LastUpdatedOn 
FROM 
(
    SELECT {Question}.[LastUpdatedOn] where {Project}.[Id] = {Question}.[ProjectId] 
    UNION ALL 
    Select {Document}.[LastUpdatedOn] where {Project}.[Id] = {Document}.[ProjectId] 
    UNION ALL 
    SELECT {Instruction}.[LastUpdatedOn] where {Project}.[Id] = {Instruction}.[ProjectId] 
) 
    A) [max_LastUpdatedOn] 

FROM {Project} 
INNER JOIN {ProjectParticipant} ON {Project}.[Id] = {ProjectParticipant}.[ProjectId] 
INNER JOIN {User} ON ({ProjectParticipant}.[UserId] = {User}.[Id] AND {User}.[Username] = @UserId) 
INNER JOIN {Question} ON {Project}.[Id] = {Question}.[ProjectId] 
INNER JOIN {Document} ON {Project}.[Id] = {Document}.[ProjectId] 
INNER JOIN {Instruction} ON {Project}.[Id] = {Instruction}.[ProjectId] 

GROUP BY {Project}.[Number], 
      {Project}.[Name], 
      {User}.[Last_Login], 
      A.[max_LastUpdatedOn] 
ORDER BY {Project}.[Number] 

获取像的多部分标识符“A.max_LastUpdatedOn”的错误不能被绑定尝试。

Answer 1

{A}不是一个OutSystems实体，因此您不应该使用大括号来引用它。花括号用于将设计时的元模型名称转换为数据库中的物理表名。

由于A是内部select语句的简单别名，只是使用A应该足以使其工作。例如：

SELECT {Project}.[Number],{Project}.[Name],{User}.[Last_Login],A.[max_LastUpdatedOn] 

UPDATE

关于有关The multi-part identifier could not be bound错误，它由东西是不是在查询的from/join源分组做。

我还没有试过下面这段代码，但这样的事情应该做的伎俩：
（另请参见关于如何选择SQL MAX of multiple columns?这里更多的方法）

SELECT {Project}.[Number], {Project}.[Name], {User}.[Last_Login], 
    CASE 
     WHEN {Question}.[LastUpdatedOn] >= {Document}.[LastUpdatedOn] AND {Question}.[LastUpdatedOn] >= {Instruction}.[LastUpdatedOn] 
     THEN {Question}.[LastUpdatedOn] 
     WHEN {Document}.[LastUpdatedOn] >= {Instruction}.[LastUpdatedOn] THEN {Document}.[LastUpdatedOn] 
     ELSE {Instruction}.[LastUpdatedOn] 
    END AS max_LastUpdatedOn 
FROM {Project} 
INNER JOIN {ProjectParticipant} ON {Project}.[Id] = {ProjectParticipant}.[ProjectId] 
INNER JOIN {User} ON ({ProjectParticipant}.[UserId] = {User}.[Id] AND {User}.[Username] = @UserId) 
INNER JOIN {Question} ON {Project}.[Id] = {Question}.[ProjectId] 
INNER JOIN {Document} ON {Project}.[Id] = {Document}.[ProjectId] 
INNER JOIN {Instruction} ON {Project}.[Id] = {Instruction}.[ProjectId] 
GROUP BY {Project}.[Number], 
     {Project}.[Name], 
     {User}.[Last_Login] 
ORDER BY {Project}.[Number]