问题
I am trying to create simple requirements management database. Basically I have 2 tables like below:
Contract_requirements with 2 columns:
CR_ReqID | Description
reqCR1 | Contract req description 1
reqCR2 | Contract req description 2
SW_requirements
Title | SW_ReqID | RootReq
SW req description 1| reqSW1 | reqCR1, reqCR2
SW req description 2| reqSW2 | reqCR1
SW req description 3| reqSW3 | reqCR2
And I would like to write query to receive such a table:
CR_ReqID |Description |where used?
reqCR1 |Contract req description 1 |reqSW1, reqSW2
reqCR2 |Contract req description 2 |reqSW1, reqSW3
Tables "Contract requirements" and "SW requirements" are in relation via column "RootReq"
Ive tried to implement code from Allen Browne http://allenbrowne.com/func-concat.html#Top
This is my query
SELECT Contract_requirements.CR_ReqID, ConcatRelated("SW_ReqID ","SW_requirements","RootReq = """ & [CR_ReqID] & """") AS Expr1
FROM Contract_requirements;
but I get error in Access
"Error3831: The multi-valued field 'RootReq' cannot be used in a WHERE or HAVING clause"
Could you guys help me to make this working? Thanks in advance
回答1:
Build a query that expands the multi-value field elements to individual records.
Query1
SELECT SW_Requirements.Title, SW_Requirements.SW_ReqID, SW_Requirements.RootReq.Value
FROM SW_Requirements;
Then use that query as source for ConcatRelated() function.
SELECT Contract_Requirements.*,
ConcatRelated("SW_ReqID","Query1","[SW_Requirements.RootReq.Value]='" & [CR_ReqID] & "'") AS WhereUsed
FROM Contract_Requirements;
Advise not to use spaces nor punctuation/special characters in naming convention.
回答2:
You can also use my DJoin function as this will accept SQL as the source, thus you won't need additional saved queries:
' Returns the joined (concatenated) values from a field of records having the same key.
' The joined values are stored in a collection which speeds up browsing a query or form
' as all joined values will be retrieved once only from the table or query.
' Null values and zero-length strings are ignored.
'
' If no values are found, Null is returned.
'
' The default separator of the joined values is a space.
' Optionally, any other separator can be specified.
'
' Syntax is held close to that of the native domain functions, DLookup, DCount, etc.
'
' Typical usage in a select query using a table (or query) as source:
'
' Select
' KeyField,
' DJoin("[ValueField]", "[Table]", "[KeyField] = " & [KeyField] & "") As Values
' From
' Table
' Group By
' KeyField
'
' The source can also be an SQL Select string:
'
' Select
' KeyField,
' DJoin("[ValueField]", "Select ValueField From SomeTable Order By SomeField", "[KeyField] = " & [KeyField] & "") As Values
' From
' Table
' Group By
' KeyField
'
' To clear the collection (cache), call DJoin with no arguments:
'
' DJoin
'
' Requires:
' CollectValues
'
' 2019-06-24, Cactus Data ApS, Gustav Brock
'
Public Function DJoin( _
Optional ByVal Expression As String, _
Optional ByVal Domain As String, _
Optional ByVal Criteria As String, _
Optional ByVal Delimiter As String = " ") _
As Variant
' Expected error codes to accept.
Const CannotAddKey As Long = 457
Const CannotReadKey As Long = 5
' SQL.
Const SqlMask As String = "Select {0} From {1} {2}"
Const SqlLead As String = "Select "
Const SubMask As String = "({0}) As T"
Const FilterMask As String = "Where {0}"
Static Values As New Collection
Dim Records As DAO.Recordset
Dim Sql As String
Dim SqlSub As String
Dim Filter As String
Dim Result As Variant
On Error GoTo Err_DJoin
If Expression = "" Then
' Erase the collection of keys.
Set Values = Nothing
Result = Null
Else
' Get the values.
' This will fail if the current criteria hasn't been added
' leaving Result empty.
Result = Values.Item(Criteria)
'
If IsEmpty(Result) Then
' The current criteria hasn't been added to the collection.
' Build SQL to lookup values.
If InStr(1, LTrim(Domain), SqlLead, vbTextCompare) = 1 Then
' Domain is an SQL expression.
SqlSub = Replace(SubMask, "{0}", Domain)
Else
' Domain is a table or query name.
SqlSub = Domain
End If
If Trim(Criteria) <> "" Then
' Build Where clause.
Filter = Replace(FilterMask, "{0}", Criteria)
End If
' Build final SQL.
Sql = Replace(Replace(Replace(SqlMask, "{0}", Expression), "{1}", SqlSub), "{2}", Filter)
' Look up the values to join.
Set Records = CurrentDb.OpenRecordset(Sql, dbOpenSnapshot)
CollectValues Records, Delimiter, Result
' Add the key and its joined values to the collection.
Values.Add Result, Criteria
End If
End If
' Return the joined values (or Null if none was found).
DJoin = Result
Exit_DJoin:
Exit Function
Err_DJoin:
Select Case Err
Case CannotAddKey
' Key is present, thus cannot be added again.
Resume Next
Case CannotReadKey
' Key is not present, thus cannot be read.
Resume Next
Case Else
' Some other error. Ignore.
Resume Exit_DJoin
End Select
End Function
' To be called from DJoin.
'
' Joins the content of the first field of a recordset to one string
' with a space as delimiter or an optional delimiter, returned by
' reference in parameter Result.
'
' 2019-06-11, Cactus Data ApS, Gustav Brock
'
Private Sub CollectValues( _
ByRef Records As DAO.Recordset, _
ByVal Delimiter As String, _
ByRef Result As Variant)
Dim SubRecords As DAO.Recordset
Dim Value As Variant
If Records.RecordCount > 0 Then
While Not Records.EOF
Value = Records.Fields(0).Value
If Records.Fields(0).IsComplex Then
' Multi-value field (or attachment field).
Set SubRecords = Records.Fields(0).Value
CollectValues SubRecords, Delimiter, Result
ElseIf Nz(Value) = "" Then
' Ignore Null values and zero-length strings.
ElseIf IsEmpty(Result) Then
' First value found.
Result = Value
Else
' Join subsequent values.
Result = Result & Delimiter & Value
End If
Records.MoveNext
Wend
Else
' No records found with the current criteria.
Result = Null
End If
Records.Close
End Sub
Full documentation can be found in my article:
Join (concat) values from one field from a table or query
If you don't have an account, browse to the link: Read the full article.
Code is also on GitHub: VBA.DJoin
来源：https://stackoverflow.com/questions/56764071/concatenating-multiple-rows-with-multiple-values-in-it-into-single-line-in-ms