SQL JOIN not returning any results

问题

I have a fairly simple join for three tables that is not returning any results. If I modify slightly I get sometime that appears jumbled (same data values in two fields). There is a Documents table from which I need the filename, a Variable table which has the variable definitions and names, and lastly I have a VariableValue table that the values for the variables are stored in. I am trying to get two values for each filename. Subject and Author. Here is the SQL call.

    SELECT DISTINCT Documents.Filename, VariableValue.ValueText AS Author,
    VariableValue.ValueText AS Subject 
    FROM Documents INNER JOIN
    VariableValue ON Documents.DocumentID = VariableValue.DocumentID INNER JOIN
    Variable AS VV1 ON VariableValue.VariableID = VV1.VariableID INNER JOIN
    Variable AS VV2 ON VariableValue.VariableID = VV2.VariableID

    WHERE (Documents.Filename LIKE N'ECO-%') AND (Documents.Deleted = 0) AND 
    (VV1.VariableName = N'Author') AND (VariableValue.ValueText <> '-') AND 
    (VV2.VariableName = N'Subject')
    ORDER BY Author asc

If I remove the (VV2.VariableName = N'Subject') I get the following result:

Filename         Author     Subject
ECO-27533.docx  billpark    billpark
ECO-27630.docx  billpark    billpark
ECO-27683.docx  billpark    billpark
ECO-27790.docx  billpark    billpark
ECO-27812.docx  billpark    billpark
ECO-27975.docx  billpark    billpark

If I remove the (VV1.VariableName = N'Author') I get the following result:

Filename        Author  Subject
ECO-28720.docx  24006   LOW PWR BM DUMP 24006 LOW PWR BM DUMP
ECO-28595.docx  24052   PIN THREAD CORRECTION   24052 PIN THREAD CORRECTION
ECO-28517.docx  24087   24087
ECO-28791.docx  25584   REV A TO B  25584 REV A TO B
ECO-28714.docx  25873   PRESSURE RELEAF ASSY    25873 PRESSURE RELEAF ASSY

What I would like is:

Filename        Author       Subject
ECO-28720.docx  billpark     LOW PWR BM DUMP

Not sure what subtle thing I am missing?

TIA.

DDL

CREATE TABLE [dbo].[Variable](
    [VariableID] [int] IDENTITY(1,1) NOT NULL,
    [VariableName] [nvarchar](255) NOT NULL,
    [VariableType] [int] NOT NULL,
    [IsDeleted] [bit] NOT NULL,
    [FlagUnique] [bit] NOT NULL,
    [FlagMandatory] [bit] NOT NULL,
    [FlagFreeUpdateAllVersion] [bit] NOT NULL CONSTRAINT [DF__Variable__FlagFr__05EEBAAE]  DEFAULT ((0)),
    [FlagFreeUpdateLatestVersion] [bit] NOT NULL CONSTRAINT [DF__Variable__FlagFr__06E2DEE7]  DEFAULT ((0)),
 CONSTRAINT [PK_Variable] PRIMARY KEY CLUSTERED 
(
    [VariableID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

AND

CREATE TABLE [dbo].[VariableValue](
    [VariableID] [int] NOT NULL,
    [DocumentID] [int] NOT NULL,
    [ProjectID] [int] NOT NULL,
    [RevisionNo] [int] NOT NULL,
    [ConfigurationID] [int] NOT NULL,
    [ValueText] [nvarchar](max) NOT NULL CONSTRAINT [DF_VariableValue_ValueText]  DEFAULT (N''),
    [ValueInt] [int] NULL,
    [ValueFloat] [float] NULL,
    [ValueDate] [datetime] NULL,
    [ValueCache] [nvarchar](64) NOT NULL CONSTRAINT [DF_VariableValue_ValueCache]  DEFAULT (''),
    [IsLongText] [bit] NOT NULL CONSTRAINT [DF_VariableValue_IsLongText]  DEFAULT ((0)),
 CONSTRAINT [PK_VariableValue] PRIMARY KEY CLUSTERED 
(
    [VariableID] ASC,
    [DocumentID] ASC,
    [ProjectID] ASC,
    [RevisionNo] ASC,
    [ConfigurationID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 80) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]

GO

ALTER TABLE [dbo].[VariableValue]  WITH NOCHECK ADD  CONSTRAINT [FK_VariableValue_DocumentConfiguration] FOREIGN KEY([ConfigurationID])
REFERENCES [dbo].[DocumentConfiguration] ([ConfigurationID])
GO

ALTER TABLE [dbo].[VariableValue] CHECK CONSTRAINT [FK_VariableValue_DocumentConfiguration]
GO

ALTER TABLE [dbo].[VariableValue]  WITH NOCHECK ADD  CONSTRAINT [FK_VariableValue_Documents] FOREIGN KEY([DocumentID])
REFERENCES [dbo].[Documents] ([DocumentID])
GO

ALTER TABLE [dbo].[VariableValue] CHECK CONSTRAINT [FK_VariableValue_Documents]
GO

ALTER TABLE [dbo].[VariableValue]  WITH CHECK ADD  CONSTRAINT [FK_VariableValue_Projects] FOREIGN KEY([ProjectID])
REFERENCES [dbo].[Projects] ([ProjectID])
GO

ALTER TABLE [dbo].[VariableValue] CHECK CONSTRAINT [FK_VariableValue_Projects]
GO

ALTER TABLE [dbo].[VariableValue]  WITH NOCHECK ADD  CONSTRAINT [FK_VariableValue_Variable] FOREIGN KEY([VariableID])
REFERENCES [dbo].[Variable] ([VariableID])
GO

ALTER TABLE [dbo].[VariableValue] CHECK CONSTRAINT [FK_VariableValue_Variable]
GO

回答1:

VariableValue.ValueText AS Author,
    VariableValue.ValueText AS Subject

You're calling the exact same alias.columnname and assigning it to both Author and Subject.

回答2:

We need to add projectID, revisionNo and ConfigurationID to the results as the PK for VariableValue is a composite key. If we don't include them, then the results could get mixed up for different projects/revsions or configurations.

So unless you have a rule that says only return the latest revision for a document... we may get multiple records back.

SELECT Documents.Filename
     , VariableValue.ProjectID
     , VariableValue.RevisionNo
     , VariableValue.ConfigurationID
     , max(Case when VV1.VariableName = N'Author' then VariableValue.ValueText END) as Author
     , max(Case when VV1.VariableName = N'Subject' then VariableValue.ValueText END)  AS Subject 
FROM Documents 
INNER JOIN VariableValue 
   ON Documents.DocumentID = VariableValue.DocumentID 
INNER JOIN Variable AS VV1 
   ON VariableValue.VariableID = VV1.VariableID 
WHERE (Documents.Filename LIKE N'ECO-%') 
  AND (Documents.Deleted = 0) 
  AND (VariableValue.ValueText <> '-') 
  AND (VV1.VariableName in (N'Author',N'Subject') 
GROUP BY Documents.Filename
     , VariableValue.ProjectID
     , VariableValue.RevisionNo
     , VariableValue.ConfigurationID

ORDER BY Author asc

回答3:

With a terrific assist from xQbert this code does it.

SELECT DISTINCT Documents.Filename, max(Case when VV1.VariableName = N'Author' then VariableValue.ValueText END) as Author, 
                                    max(Case when VV1.VariableName = N'Subject' then VariableValue.ValueText END) AS Description 
FROM Documents INNER JOIN
                         VariableValue ON Documents.DocumentID = VariableValue.DocumentID INNER JOIN
                         Variable AS VV1 ON VariableValue.VariableID = VV1.VariableID INNER JOIN
                         Variable AS VV2 ON VariableValue.VariableID = VV2.VariableID
WHERE (Documents.Filename LIKE N'ECO-%') AND (Documents.Deleted = 0) AND  (VV1.VariableName in (N'Author',N'Subject') AND (VariableValue.ValueText <> '-'))
Group BY Documents.Filename
ORDER BY Author asc

来源：https://stackoverflow.com/questions/46301060/sql-join-not-returning-any-results

标签

sql-server

inner-join