代码：
DECLARE @Table TABLE
(
[Id] INT IDENTITY(1, 1),
[Val] NVARCHAR(MAX)
)
INSERT INTO @Table
SELECT N'123451234512345'
UNION ALL
SELECT N'ABC@ABC.comABC@ABC.comABC@ABC.com'
当前输出：
Id Val
---------------------------------------
1 123451234512345
2 ABC@ABC.comABC@ABC.comABC@ABC.com
所需的输出：
Id Val
------------------
1 12345
2 ABC@ABC.com
目标：删除Val列中的字符串（无可用分隔符）。如果有一个定界符，我可以拆分和重复，但没有一个，我不知道如何以最有效的方式来实现。该值可以在一列中重复0到很多次。
答案 0 :(得分：3)
我不会说这确实有效，但是您可以使用递归CTE：
with cte as (
select str, convert(varchar(max), left(str, 1)) as substr, 1 as lev
from t
union all
select str, convert(varchar(max), left(str, lev)) as substr, 1 + lev
from cte
where lev <= len(str)
)
select x.*
from t cross apply
(select top (1) cte.*
from cte
where cte.str = t.str and
replace(cte.str, cte.substr, '') = ''
order by cte.lev asc
) x;
Here是db <>小提琴。
答案 1 :(得分：1)
假设[Val]中至少有两个字符，请尝试以下UDF：
create function Dedup(@InCol nvarchar(max))
returns nvarchar(max) as
begin
declare @i int = 2
while charindex(left(@InCol, @i), @InCol, @i+1)>0 select @i += 1
select @i = case when left(@InCol, @i-1) = right(@InCol, @i-1) then @i-1 else len(@InCol) end
return left(@InCol, @i)
end
为
select Id, dbo.Dedup(Val) as Val from @Table
答案 2 :(得分：1)
正如戈登所说-递归CTE可以工作，但是速度很慢。对于讨厌的快速解决方案，您可以使用dbo.rangeAB（本文底部的代码）。首先创建逻辑以根据需要“消除”字符串。
-- Logic to create a function to "deduplicate" the values
DECLARE @string VARCHAR(8000) = '123451234512345'; -- 'ABC@ABC.comABC@ABC.comABC@ABC.com';
SELECT fnDedupe.itemLength, fnDedupe.item
FROM
(
SELECT TOP (1) r.OP, lg.t
FROM dbo.rangeAB(1,LEN(@string),1,1) AS r
CROSS APPLY (VALUES(SUBSTRING(@string,1,r.OP-1))) AS lg(t)
CROSS APPLY (VALUES(CHARINDEX(lg.t,@string,r.OP))) AS f(x)
WHERE f.x > 0
ORDER BY r.RN
) AS fnDedupe(itemLength,item);
这将返回：
itemLength item
----------- ------
6 12345
接下来，我们使用APPLY将其应用于您的表；您将用t.v替换@string：
DECLARE @Table TABLE
(
[Id] INT IDENTITY(1, 1),
[Val] NVARCHAR(MAX)
);
INSERT INTO @Table
SELECT N'123451234512345' UNION ALL SELECT N'ABC@ABC.comABC@ABC.comABC@ABC.com';
SELECT t.Id, t.Val, fnDedupe.item
FROM @Table AS t
CROSS APPLY
(
SELECT TOP (1) r.OP, lg.t
FROM dbo.rangeAB(1,LEN(t.val),1,1) AS r
CROSS APPLY (VALUES(SUBSTRING(t.val,1,r.OP-1))) AS lg(t)
CROSS APPLY (VALUES(CHARINDEX(lg.t,t.val,r.OP))) AS f(x)
WHERE f.x > 0
ORDER BY r.RN
) AS fnDedupe(itemLength,item);
这将返回：
Id Val item
----- --------------------------------------- --------------
1 123451234512345 12345
2 ABC@ABC.comABC@ABC.comABC@ABC.com ABC@ABC.com
这是范围AB：
CREATE FUNCTION dbo.rangeAB
(
@low bigint,
@high bigint,
@gap bigint,
@row1 bit
)
/****************************************************************************************
[Purpose]:
Creates up to 531,441,000,000 sequentia1 integers numbers beginning with @low and ending
with @high. Used to replace iterative methods such as loops, cursors and recursive CTEs
to solve SQL problems. Based on Itzik Ben-Gan's getnums function with some tweeks and
enhancements and added functionality. The logic for getting rn to begin at 0 or 1 is
based comes from Jeff Moden's fnTally function.
The name range because it's similar to clojure's range function. The name "rangeAB" as
used because "range" is a reserved SQL keyword.
[Author]: Alan Burstein
[Compatibility]:
SQL Server 2008+ and Azure SQL Database
[Syntax]:
SELECT r.RN, r.OP, r.N1, r.N2
FROM dbo.rangeAB(@low,@high,@gap,@row1) AS r;
[Parameters]:
@low = a bigint that represents the lowest value for n1.
@high = a bigint that represents the highest value for n1.
@gap = a bigint that represents how much n1 and n2 will increase each row; @gap also
represents the difference between n1 and n2.
@row1 = a bit that represents the first value of rn. When @row = 0 then rn begins
at 0, when @row = 1 then rn will begin at 1.
[Returns]:
Inline Table Valued Function returns:
rn = bigint; a row number that works just like T-SQL ROW_NUMBER() except that it can
start at 0 or 1 which is dictated by @row1.
op = bigint; returns the "opposite number that relates to rn. When rn begins with 0 and
ends with 10 then 10 is the opposite of 0, 9 the opposite of 1, etc. When rn begins
with 1 and ends with 5 then 1 is the opposite of 5, 2 the opposite of 4, etc...
n1 = bigint; a sequential number starting at the value of @low and incrimentingby the
value of @gap until it is less than or equal to the value of @high.
n2 = bigint; a sequential number starting at the value of @low+@gap and incrimenting
by the value of @gap.
[Dependencies]:
N/A
[Developer Notes]:
1. The lowest and highest possible numbers returned are whatever is allowable by a
bigint. The function, however, returns no more than 531,441,000,000 rows (8100^3).
2. @gap does not affect rn, rn will begin at @row1 and increase by 1 until the last row
unless its used in a query where a filter is applied to rn.
3. @gap must be greater than 0 or the function will not return any rows.
4. Keep in mind that when @row1 is 0 then the highest row-number will be the number of
rows returned minus 1
5. If you only need is a sequential set beginning at 0 or 1 then, for best performance
use the RN column. Use N1 and/or N2 when you need to begin your sequence at any
number other than 0 or 1 or if you need a gap between your sequence of numbers.
6. Although @gap is a bigint it must be a positive integer or the function will
not return any rows.
7. The function will not return any rows when one of the following conditions are true:
* any of the input parameters are NULL
* @high is less than @low
* @gap is not greater than 0
To force the function to return all NULLs instead of not returning anything you can
add the following code to the end of the query:
UNION ALL
SELECT NULL, NULL, NULL, NULL
WHERE NOT (@high&@low&@gap&@row1 IS NOT NULL AND @high >= @low AND @gap > 0)
This code was excluded as it adds a ~5% performance penalty.
8. There is no performance penalty for sorting by rn ASC; there is a large performance
penalty for sorting in descending order WHEN @row1 = 1; WHEN @row1 = 0
If you need a descending sort the use op in place of rn then sort by rn ASC.
Best Practices:
--===== 1. Using RN (rownumber)
-- (1.1) The best way to get the numbers 1,2,3...@high (e.g. 1 to 5):
SELECT RN FROM dbo.rangeAB(1,5,1,1);
-- (1.2) The best way to get the numbers 0,1,2...@high-1 (e.g. 0 to 5):
SELECT RN FROM dbo.rangeAB(0,5,1,0);
--===== 2. Using OP for descending sorts without a performance penalty
-- (2.1) The best way to get the numbers 5,4,3...@high (e.g. 5 to 1):
SELECT op FROM dbo.rangeAB(1,5,1,1) ORDER BY rn ASC;
-- (2.2) The best way to get the numbers 0,1,2...@high-1 (e.g. 5 to 0):
SELECT op FROM dbo.rangeAB(1,6,1,0) ORDER BY rn ASC;
--===== 3. Using N1
-- (3.1) To begin with numbers other than 0 or 1 use N1 (e.g. -3 to 3):
SELECT N1 FROM dbo.rangeAB(-3,3,1,1);
-- (3.2) ROW_NUMBER() is built in. If you want a ROW_NUMBER() include RN:
SELECT RN, N1 FROM dbo.rangeAB(-3,3,1,1);
-- (3.3) If you wanted a ROW_NUMBER() that started at 0 you would do this:
SELECT RN, N1 FROM dbo.rangeAB(-3,3,1,0);
--===== 4. Using N2 and @gap
-- (4.1) To get 0,10,20,30...100, set @low to 0, @high to 100 and @gap to 10:
SELECT N1 FROM dbo.rangeAB(0,100,10,1);
-- (4.2) Note that N2=N1+@gap; this allows you to create a sequence of ranges.
-- For example, to get (0,10),(10,20),(20,30).... (90,100):
SELECT N1, N2 FROM dbo.rangeAB(0,90,10,1);
-- (4.3) Remember that a rownumber is included and it can begin at 0 or 1:
SELECT RN, N1, N2 FROM dbo.rangeAB(0,90,10,1);
[Examples]:
--===== 1. Generating Sample data (using rangeAB to create "dummy rows")
-- The query below will generate 10,000 ids and random numbers between 50,000 and 500,000
SELECT
someId = r.rn,
someNumer = ABS(CHECKSUM(NEWID())%450000)+50001
FROM rangeAB(1,10000,1,1) r;
--===== 2. Create a series of dates; rn is 0 to include the first date in the series
DECLARE @startdate DATE = '20180101', @enddate DATE = '20180131';
SELECT r.rn, calDate = DATEADD(dd, r.rn, @startdate)
FROM dbo.rangeAB(1, DATEDIFF(dd,@startdate,@enddate),1,0) r;
GO
--===== 3. Splitting (tokenizing) a string with fixed sized items
-- given a delimited string of identifiers that are always 7 characters long
DECLARE @string VARCHAR(1000) = 'A601225,B435223,G008081,R678567';
SELECT
itemNumber = r.rn, -- item's ordinal position
itemIndex = r.n1, -- item's position in the string (it's CHARINDEX value)
item = SUBSTRING(@string, r.n1, 7) -- item (token)
FROM dbo.rangeAB(1, LEN(@string), 8,1) r;
GO
--===== 4. Splitting (tokenizing) a string with random delimiters
DECLARE @string VARCHAR(1000) = 'ABC123,999F,XX,9994443335';
SELECT
itemNumber = ROW_NUMBER() OVER (ORDER BY r.rn), -- item's ordinal position
itemIndex = r.n1+1, -- item's position in the string (it's CHARINDEX value)
item = SUBSTRING
(
@string,
r.n1+1,
ISNULL(NULLIF(CHARINDEX(',',@string,r.n1+1),0)-r.n1-1, 8000)
) -- item (token)
FROM dbo.rangeAB(0,DATALENGTH(@string),1,1) r
WHERE SUBSTRING(@string,r.n1,1) = ',' OR r.n1 = 0;
-- logic borrowed from: http://www.sqlservercentral.com/articles/Tally+Table/72993/
--===== 5. Grouping by a weekly intervals
-- 5.1. how to create a series of start/end dates between @startDate & @endDate
DECLARE @startDate DATE = '1/1/2015', @endDate DATE = '2/1/2015';
SELECT
WeekNbr = r.RN,
WeekStart = DATEADD(DAY,r.N1,@StartDate),
WeekEnd = DATEADD(DAY,r.N2-1,@StartDate)
FROM dbo.rangeAB(0,datediff(DAY,@StartDate,@EndDate),7,1) r;
GO
-- 5.2. LEFT JOIN to the weekly interval table
BEGIN
DECLARE @startDate datetime = '1/1/2015', @endDate datetime = '2/1/2015';
-- sample data
DECLARE @loans TABLE (loID INT, lockDate DATE);
INSERT @loans SELECT r.rn, DATEADD(dd, ABS(CHECKSUM(NEWID())%32), @startDate)
FROM dbo.rangeAB(1,50,1,1) r;
-- solution
SELECT
WeekNbr = r.RN,
WeekStart = dt.WeekStart,
WeekEnd = dt.WeekEnd,
total = COUNT(l.lockDate)
FROM dbo.rangeAB(0,datediff(DAY,@StartDate,@EndDate),7,1) r
CROSS APPLY (VALUES (
CAST(DATEADD(DAY,r.N1,@StartDate) AS DATE),
CAST(DATEADD(DAY,r.N2-1,@StartDate) AS DATE))) dt(WeekStart,WeekEnd)
LEFT JOIN @loans l ON l.lockDate BETWEEN dt.WeekStart AND dt.WeekEnd
GROUP BY r.RN, dt.WeekStart, dt.WeekEnd ;
END;
--===== 6. Identify the first vowel and last vowel in a along with their positions
DECLARE @string VARCHAR(200) = 'This string has vowels';
SELECT TOP(1) position = r.rn, letter = SUBSTRING(@string,r.rn,1)
FROM dbo.rangeAB(1,LEN(@string),1,1) r
WHERE SUBSTRING(@string,r.rn,1) LIKE '%[aeiou]%'
ORDER BY r.rn;
-- To avoid a sort in the execution plan we'll use op instead of rn
SELECT TOP(1) position = r.op, letter = SUBSTRING(@string,r.op,1)
FROM dbo.rangeAB(1,LEN(@string),1,1) r
WHERE SUBSTRING(@string,r.rn,1) LIKE '%[aeiou]%'
ORDER BY r.rn;
---------------------------------------------------------------------------------------
[Revision History]:
Rev 00 - 20140518 - Initial Development - Alan Burstein
Rev 01 - 20151029 - Added 65 rows to make L1=465; 465^3=100.5M. Updated comment section
- Alan Burstein
Rev 02 - 20180613 - Complete re-design including opposite number column (op)
Rev 03 - 20180920 - Added additional CROSS JOIN to L2 for 530B rows max - Alan Burstein
****************************************************************************************/
RETURNS TABLE WITH SCHEMABINDING AS RETURN
WITH L1(N) AS
(
SELECT 1
FROM (VALUES
(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),
(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),
(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),
(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),
(0),(0)) T(N) -- 90 values
),
L2(N) AS (SELECT 1 FROM L1 a CROSS JOIN L1 b CROSS JOIN L1 c),
iTally AS (SELECT rn = ROW_NUMBER() OVER (ORDER BY (SELECT 1)) FROM L2 a CROSS JOIN L2 b)
SELECT
r.RN,
r.OP,
r.N1,
r.N2
FROM
(
SELECT
RN = 0,
OP = (@high-@low)/@gap,
N1 = @low,
N2 = @gap+@low
WHERE @row1 = 0
UNION ALL -- COALESCE required in the TOP statement below for error handling purposes
SELECT TOP (ABS((COALESCE(@high,0)-COALESCE(@low,0))/COALESCE(@gap,0)+COALESCE(@row1,1)))
RN = i.rn,
OP = (@high-@low)/@gap+(2*@row1)-i.rn,
N1 = (i.rn-@row1)*@gap+@low,
N2 = (i.rn-(@row1-1))*@gap+@low
FROM iTally AS i
ORDER BY i.rn
) AS r
WHERE @high&@low&@gap&@row1 IS NOT NULL AND @high >= @low AND @gap > 0;