Ms Access Query：通过查询连接行

Question

Suppose I have table in Ms Access with following information:

ColumnA ColumnB
1       abc
1       pqr
1       xyz
2       efg
2       hij
3       asd

My question is, how can I concatenate the values in the second column to a row value based on the first column. The query results that I want is as follows:

ColumnA ColumnB
1       abc, pqr, xyz
2       efg, hij
3       asd

I want to achieve this through a query. Can someone help me attain this?

Answer 1

You need a function to do the concatenation.

Microsoft Access condense multiple lines in a table

Example using your data:

Select T.ColumnA
  , GetList("Select ColumnB From Table1 As T1 Where T1.ColumnA = " & [T].[ColumnA],"",", ") AS ColumnBItems
From Table1 AS T
Group By T.ColumnA;

Answer 2

Here's an outstanding link re: how to do this from within SQL by calling a function. The instructions are exceptionally clear & the function is written for you so you can just copy, paste & go. Even someone with no knowledge of VB can easily implement it: Concatenate values from related records

Answer 3

this can be very difficult to obtain. If you MUST do it in a query and not a function, the problem that you will run into is the limit of the number of rows you can concatenate into one column. So far the only way that i have found to achieve this is via iif statements.

SELECT 
test1.ColumnA AS ColumnA, 
First([test1].[ColumnB]) & IIf(Count([test1].[ColumnB])>1,"," & Last([test1].[ColumnB])) AS ColumnB
FROM test1
GROUP BY test1.ColumnA;

returns:

ColumnA  ColumnB 
1      abc,xyz 
2      efg,hij 
3      asd

This will return the first and the last only, but I'm sure with a little work you could work out the Choose function, but like I said you would have to add more iif statements for each additional item you want to add, hence the limitation.

Answer 4

The table could have a sequence column, which gives it a unique primary key of ColumnA-sequence:

table: t1
ColumnA sequence ColumnB
1       1        abc
1       2        pqr
1       3        xyz
2       1        efg
2       2        hij
3       1        asd

And a Crosstab could be created:

query: x1
TRANSFORM Min([columnB] & ", ") AS Expr1
SELECT t1.columnA
FROM t1
GROUP BY t1.columnA
PIVOT t1.sequence;

columnA 1    2    3
1       abc, pqr, xyz,
2       efg, hij,
3       asd,

Then a final query can combine the columns and remove the last comma:

SELECT x1.columnA, Left([1] & [2] & [3],Len([1] & [2] & [3])-2) AS columnB FROM x1;

columnA columnB
1       abc, pqr, xyz
2       efg, hij
3       asd

To automate filling in the sequence, the following VBA code can be used:

Sub fill_sequence_t1()
  Dim i: i = 1
  Do While DCount("*", "t1", "sequence IS NULL") > 0
    DoCmd.RunSQL "SELECT t1.columnA, Min(t1.columnB) AS columnB_min INTO t2" & _
                 " FROM t1 WHERE t1.sequence IS NULL GROUP BY t1.columnA;"
    DoCmd.RunSQL "UPDATE t1 INNER JOIN t2 ON (t1.columnA = t2.columnA)" & _
                 " AND (t1.columnB = t2.columnB_min) SET t1.sequence=" & i
    CurrentDb.TableDefs.Delete "t2"
    i = i + 1
  Loop
End Sub