sql - t-sql 使用 csv 字符串查找特定值

Question

我需要一些关于 SQL 查询的帮助。我有一列将值存储为逗号分隔值。

我需要编写一个查询，在列中的每个值中找到第三个分隔项。

是否可以在 Select 语句中执行此操作？例如：列值：josh,Reg01,False,a0-t0,22/09/2010

所以我需要False从上面的字符串中获取第三个值（即）。

Answer 1

是的。

@s你的弦在哪里...

select 
    SUBSTRING (@s,
    CHARINDEX(',',@s,CHARINDEX(',',@s)+1)+1,
    CHARINDEX(',',@s,CHARINDEX(',',@s,CHARINDEX(',',@s)+1)+1)
          -CHARINDEX(',',@s,CHARINDEX(',',@s)+1)-1)

或者更笼统地...

;with cte as 
(
    select 1 as Item, 1 as Start, CHARINDEX(',',@s, 1) as Split
    union all
    select cte.Item+1, cte.Split+1, nullif(CHARINDEX(',',@s, cte.Split+1),0) as Split
    from cte
    where cte.Split<>0  
)   
select SUBSTRING(@s, start,isnull(split,len(@s)+1)-start) 
from cte 
where Item = 3

现在正确存储您的数据:)

Answer 2

试试这个（假设 SQL Server 2005+）

DECLARE @t TABLE(ColumnValue VARCHAR(50))
INSERT INTO @t(ColumnValue) SELECT 'josh,Reg01,False,a0-t0,22/09/2010'
INSERT INTO @t(ColumnValue) SELECT 'mango,apple,bannana,grapes'
INSERT INTO @t(ColumnValue) SELECT 'stackoverflow'

SELECT ThirdValue = splitdata
FROM(
        SELECT 
            Rn = ROW_NUMBER() OVER(PARTITION BY ColumnValue ORDER BY (SELECT 1))
            ,X.ColumnValue
            ,Y.splitdata 
        FROM
         (
            SELECT *,
            CAST('<X>'+REPLACE(F.ColumnValue,',','</X><X>')+'</X>' AS XML) AS xmlfilter FROM @t F
         )X
         CROSS APPLY
         ( 
            SELECT fdata.D.value('.','varchar(50)') AS splitdata 
            FROM X.xmlfilter.nodes('X') as fdata(D)
         ) Y
    )X WHERE X.Rn = 3

//结果

第三值

False
bannana

此外，您的问题也不是很清楚您使用的是什么版本的 SQL Server。如果您使用的是 SQL SERVER 2000，则可以继续使用以下方法。

第 1 步：创建一个数字表

CREATE TABLE dbo.Numbers
(
   N INT NOT NULL PRIMARY KEY
);
GO

DECLARE @rows AS INT;
SET @rows = 1;

INSERT INTO dbo.Numbers VALUES(1);
WHILE(@rows <= 10000)
BEGIN
   INSERT INTO dbo.Numbers SELECT N + @rows FROM dbo.Numbers;
   SET @rows = @rows * 2;
END 

第 2 步：应用下面的查询

DECLARE @t TABLE(ColumnValue VARCHAR(50))
INSERT INTO @t(ColumnValue) SELECT 'josh,Reg01,False,a0-t0,22/09/2010'
INSERT INTO @t(ColumnValue) SELECT 'mango,apple,bannana,grapes'
INSERT INTO @t(ColumnValue) SELECT 'stackoverflow'

--Declare a table variable to put the identity column and store the indermediate results
DECLARE @tempT TABLE(Id INT IDENTITY,ColumnValue VARCHAR(50),SplitData VARCHAR(50))

-- Insert the records into the table variable
INSERT INTO @tempT
SELECT  
    ColumnValue
    ,SUBSTRING(ColumnValue, Numbers.N,CHARINDEX(',', ColumnValue + ',', Numbers.N) - Numbers.N) AS splitdata 
FROM @t 
JOIN Numbers ON Numbers.N <= DATALENGTH(ColumnValue) + 1  
AND SUBSTRING(',' + ColumnValue, Numbers.N, 1) = ','  

--Project the filtered records

SELECT ThirdValue = X.splitdata
FROM
--The co-related subquery does the ROW_NUMBER() OVER(PARTITION BY ColumnValue)
(SELECT 
  Rn = (SELECT COUNT(*) 
        FROM @tempT t2 
        WHERE t2.ColumnValue=t1.ColumnValue 
        AND t2.Id<=t1.Id)
 ,t1.ColumnValue
 ,t1.splitdata
FROM @tempT t1)X
WHERE X.Rn =3

- 结果

第三值

False
bannana

您也可以将 Master..spt_Values 用于您的数字表

DECLARE @t TABLE(ColumnValue VARCHAR(50))
INSERT INTO @t(ColumnValue) SELECT 'josh,Reg01,False,a0-t0,22/09/2010'
INSERT INTO @t(ColumnValue) SELECT 'mango,apple,bannana,grapes'
INSERT INTO @t(ColumnValue) SELECT 'stackoverflow'

--Declare a table variable to put the identity column and store the indermediate results
DECLARE @tempT TABLE(Id INT IDENTITY,ColumnValue VARCHAR(50),SplitData VARCHAR(50))

-- Insert the records into the table variable
INSERT INTO @tempT
SELECT  
    ColumnValue
    ,SUBSTRING(ColumnValue, Number ,CHARINDEX(',', ColumnValue + ',', Number ) - Number) AS splitdata 
FROM @t 
JOIN master..spt_values ON Number <= DATALENGTH(ColumnValue) + 1  AND type='P'
AND SUBSTRING(',' + ColumnValue, Number , 1) = ','  

--Project the filtered records
SELECT ThirdValue = X.splitdata
FROM
--The co-related subquery does the ROW_NUMBER() OVER(PARTITION BY ColumnValue)
(SELECT 
  Rn = (SELECT COUNT(*) 
        FROM @tempT t2 
        WHERE t2.ColumnValue=t1.ColumnValue 
        AND t2.Id<=t1.Id)
 ,t1.ColumnValue
 ,t1.splitdata
FROM @tempT t1)X
WHERE X.Rn =3

您可以从

1）系统表table master..spt_values的用途是什么，其值的含义是什么？

2)为什么（以及如何）使用 master..spt_values 拆分列？

Answer 3

你真的需要像 String.Split(',')(2) 这样的东西，不幸的是在 SQL 中不存在，但这可能对你有帮助

Answer 4

您可以使用此解决方案和其他解决方案进行一些测试，但是，我相信在这种情况下使用 XML 几乎总是可以为您提供最佳性能并确保更少的编码：

DECLARE @InPutCSV NVARCHAR(2000)= 'josh,Reg01,False,a0-t0,22/09/2010'
DECLARE @ValueIndexToGet INT=3
DECLARE @XML XML =  CAST ('<d>' + REPLACE(@InPutCSV, ',', '</d><d>') + '</d>' AS XML);

WITH CTE(RecordNumber,Value) AS
(
     SELECT  ROW_NUMBER() OVER(ORDER BY T.v.value('.', 'NVARCHAR(100)') DESC) AS RecordNumber
             ,T.v.value('.', 'NVARCHAR(100)') AS Value
     FROM @XML.nodes('/d') AS T(v)
)
SELECT Value
FROM CTE WHERE RecordNumber=@ValueIndexToGet

我可以确认从具有 100 000 个值的 CSV 字符串中获取值需要 1 秒。