如何根據一列特殊的文字串的位置來獲得價值

Question

我有這樣

Col1     Col2 
Adam     1 
Barbara, Catherina  1 
Barbara, Catherina  2 
Adam, Catherina   1 
Adam, Catherina   2 
Barbara, Adam, Daniela 1 
Barbara, Adam, Daniela 2 
Barbara, Adam, Daniela 3 

表需要一個select語句填充COL3像圖所示

Col1     Col2 Col 3 
Adam     1 Adam 
Barbara, Catherina  1 Barbara 
Barbara, Catherina  2 Catherina 
Adam, Catherina   1 Adam 
Adam, Catherina   2 Catherina 
Barbara, Adam, Daniela 1 Barbara 
Barbara, Adam, Daniela 2 Adam 
Barbara, Adam, Daniela 3 Daniela 

我嘗試使用SUITTRING & CHARINDEX，但無法解決這個問題。需要一個SQL，我們可以傳遞Col2值並填充Col3。

請幫忙。 謝謝，Vikram

Answer 1

具有分析/拆分功能和交叉應用。

我應該補充一點，如果你不能使用或不想使用UDF，那麼解析可以很容易地移植到CROSS APPLY中。

Declare @YourTable table (Col1 varchar(25),Col2 int) 
Insert Into @YourTable Values 
('A',  1), 
('B,C', 1), 
('B,C', 2), 
('A,C', 1), 
('A,C', 2), 
('B,A,D', 1), 
('B,A,D', 2), 
('B,A,D', 3) 

Select A.* 
     ,Col3 = B.RetVal 
From @YourTable A 
Cross Apply (Select * from [dbo].[udf-Str-Parse](A.Col1,',') where RetSeq=A.Col2) B 

返回

Col1 Col2 Col3 
A  1  A 
B,C  1  B 
B,C  2  C 
A,C  1  A 
A,C  2  C 
B,A,D 1  B 
B,A,D 2  A 
B,A,D 3  D 

的UDF如果需要

CREATE FUNCTION [dbo].[udf-Str-Parse] (@String varchar(max),@Delimiter varchar(10)) 
Returns Table 
As 
Return ( 
    Select RetSeq = Row_Number() over (Order By (Select null)) 
      ,RetVal = LTrim(RTrim(B.i.value('(./text())[1]', 'varchar(max)'))) 
    From (Select x = Cast('<x>'+ Replace(@String,@Delimiter,'</x><x>')+'</x>' as xml).query('.')) as A 
    Cross Apply x.nodes('x') AS B(i) 
); 
--Select * from [dbo].[udf-Str-Parse]('Dog,Cat,House,Car',',') 
--Select * from [dbo].[udf-Str-Parse]('John Cappelletti was here',' ') 

只是爲了好玩，這是NON-UDF版本

Select A.* 
     ,Col3 = B.RetVal 
From @YourTable A 
Cross Apply (
       Select * From( 
        Select RetSeq = Row_Number() over (Order By (Select null)) 
          ,RetVal = LTrim(RTrim(B.i.value('(./text())[1]', 'varchar(max)'))) 
        From (Select x = Cast('<x>'+ Replace(A.Col1,',','</x><x>')+'</x>' as xml).query('.')) as A 
        Cross Apply x.nodes('x') AS B(i) 
       ) C where RetSeq=A.Col2 
      ) B 

Answer 2

您可以創建一個函數，該函數獲取字符串（col1）和文本索引（col2）並返回正確的值。查詢應該是這樣的：

SELECT col1, col2, GetElement(co1, col2) as col3 
FROM table 

的GetElement可以使用WHILE循環找到該值。僞代碼：

index = 1 
while index < col2 
charindex of the ',' 
if index == col2 substring to the next ',' and return 
else index = index + 1 and remove the substring from beginning to the charindex of ',' 

Answer 3

這一個只適用於SQL 2016和Azure的SQL數據庫（more on STRING_SPLIT）

DECLARE @DaTable TABLE (Col1 varchar(32),Col2 int) 
INSERT INTO @DaTable 
VALUES 
('A',  1), 
('B,C', 1), 
('B,C', 2), 
('A,C', 1), 
('A,C', 2), 
('B,A,D', 1), 
('B,A,D', 2), 
('B,A,D', 3) 

SELECT S.* 
     ,Col3 = T.Value 
From @DaTable S 
Cross Apply (SELECT * FROM 
(Select Value, Row_Number() OVER (ORDER BY (SELECT 0)) AS RowNum from STRING_SPLIT(S.Col1,',')) AS ss 
where ss.RowNum = S.Col2) AS T 

注意對Azure的SQL數據庫：

的STRING_SPLIT功能僅在兼容性可用級別130. [...] 請注意，即使在新的Azure SQL數據庫中，兼容級別120也可能是默認級別。