基于 1 个或多个可能的分隔符的 SQL 拆分列并插入新表

Question

我目前正在研究 MS-Access 2010 中的 SQl，它可以基于分隔符 (,) 拆分列。在我要拆分的列中可以有零、一、二或三分隔符。我发现如果只有一个分隔符（请参阅问题末尾的 SQL），但如果有多个分隔符，我可以拆分列。

SQL 基于下表。该表中填满了表中可能出现的数据。

ID         column_value
---------------------
1          2, 44
2          1
3          8, 9, 4
4          7

我想以创建这样的新表的方式拆分“值”列。 “ID”列相同不是问题，因为这不会是PK。

ID         value
---------------------
1          2
1          44
2          1
3          8
3          9
3          4
4          7

我试图从 this question 更改 SQL，但它仅在只有 1 个分隔符（，）时才有效，因为事实上它使用函数 LEFT 和 MID。如果列中有超过 1 个分隔符，我无法找到如何以可以拆分的方式更改它。如果有一个分隔符，我用来分割的SQL：

  select * into importeddata
from (SELECT column_value, id
  FROM SourceData
  WHERE InStr(column_value, ',') = 1
  UNION ALL
  SELECT Left(column_value, InStr(column_value, ',') - 1), id
  FROM SourceData
  WHERE InStr(column_value, ',') > 0
  UNION ALL
  SELECT mid(column_value, InStr(column_value, ',')+1 ), id
  FROM SourceData
  WHERE InStr(column_value, ',') > 0) AS CleanedUp;

如果有多个分隔符，有人知道如何拆分列吗？

Answer 1

要拆分并获取特定值，我更喜欢使用自定义函数。

Public Function SplitString(str As String, delimiter As String, count As Integer) As String
    Dim strArr() As String
    strArr = Split(str, delimiter, count + 1)
    count = count - 1 'zero-based
    If UBound(strArr) >= count Then
        SplitString = strArr(count)
    End If
End Function

在此之后，您可以将 SQL 调整为以下内容：

SELECT * INTO importeddata
FROM (
SELECT SplitString(column_value, ',', 1), id
FROM SourceData
WHERE SplitString(column_value, ',', 1) <> ''
UNION ALL
SELECT SplitString(column_value, ',', 2), id
FROM SourceData
WHERE SplitString(column_value, ',', 2) <> ''
UNION ALL
SELECT SplitString(column_value, ',', 3), id
FROM SourceData
WHERE SplitString(column_value, ',', 3) <> ''
) AS A

如果您真的想要一个全 SQL 的解决方案，让我向您演示如何实现这一点，以及为什么这是一个糟糕的计划。

对于本示例，我编写了以下代码来自动生成适当的 SQL 表达式

Public Sub GenerateSQLSplit(str As String, Delimiter As String, Count As Integer)
    Dim i As Integer
    If Count = 1 Then
        Debug.Print "IIf(InStr(1, " & str & ", " & Delimiter & ") = -1, " & str & ", Left(" & str & ", InStr(1, " & str & ", " & Delimiter & ") - 1))"
    Else
        Dim strPrevious As String
        Dim strNext As String
        strPrevious = "InStr(1, " & str & "," & Delimiter & ")"
        i = Count - 1
        Do While i <> 1
            strPrevious = "InStr(" & strPrevious & " + Len(" & Delimiter & "), " & str & "," & Delimiter & ")"
            i = i - 1
        Loop
        strNext = "InStr(" & strPrevious & " + Len(" & Delimiter & "), " & str & " , " & Delimiter & ")"
        Debug.Print "IIf( " & strPrevious & "> 0, IIf(" & strNext & " < 1, Mid(" & str & ", " & strPrevious & " + Len(" & Delimiter & ")), Mid(" & str & ", " & strPrevious & " + Len(" & Delimiter & "), " & strNext & " - " & strPrevious & " - Len(" & Delimiter & "))), """") "
    End If
End Sub

让我们用例子来生成一个简单的拆分：我想要以下字符串的第 6 个元素：1,2,3,4,5,6,7

要生成字符串，在即时窗口中：

GenerateSQLSplit "'1,2,3,4,5,6,7'", "','", 6

导致以下表达式返回该字符串的第 6 个元素（仅限 SQL）：

IIf( InStr(InStr(InStr(InStr(InStr(1, '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',')> 0, IIf(InStr(InStr(InStr(InStr(InStr(InStr(1, '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7' , ',') < 1, Mid('1,2,3,4,5,6,7', InStr(InStr(InStr(InStr(InStr(1, '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(',')), Mid('1,2,3,4,5,6,7', InStr(InStr(InStr(InStr(InStr(1, '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), InStr(InStr(InStr(InStr(InStr(InStr(1, '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7'
,',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7' , ',') - InStr(InStr(InStr(InStr(InStr(1, '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') + Len(','), '1,2,3,4,5,6,7',',') - Len(','))), "") 

将SELECT 附加到它的开头，并将其作为查询执行，它按预期返回6。只有你有一个完全可怕的查询，而使用 UDF 你只会有SELECT SplitString("1,2,3,4,5,6,7", ",", 6)

当然，您可以使用GenerateSQLSplit 创建查询（如果项目不在字符串中，我确保它返回一个空字符串，因此您可以使用它来测试是否存在第 n 个元素）。不过我不推荐它，因为查询会很长、效率低且难以维护。