How to SELECT string between second and third instance of ",,"? - sql

Question

I am trying to get string between second and third instance of ",," using SQL SELECT.
Apparently functions substring and charindex are useful, and I have tried them but the problem is that I need the string between those specific ",,"s and the length of the strings between them can change.
Can't find working example anywhere.
Here is an example:
Table: test
Column: Column1
Row1: cat1,,cat2,,cat3,,cat4,,cat5
Row2: dogger1,,dogger2,,dogger3,,dogger4,,dogger5
Result: cat3dogger3
Here is my closest attempt, it works if the strings are same length every time, but they aren't:
SELECT SUBSTRING(column1,LEN(LEFT(column1,CHARINDEX(',,', column1,12)+2)),LEN(column1) - LEN(LEFT(column1,CHARINDEX(',,', column1,20)+2)) - LEN(RIGHT(column1,CHARINDEX(',,', (REVERSE(column1)))))) AS column1
FROM testi

Answer 1

Just repeat sub-string 3 times, each time moving onto the next ",," e.g.
select
-- Substring till the third ',,'
substring(z.col1, 1, patindex('%,,%',z.col1)-1)
from (values ('cat1,,cat2,,cat3,,cat4,,cat5'),('dogger1,,dogger2,,dogger3,,dogger4,,dogger5')) x (col1)
-- Substring from the first ',,'
cross apply (values (substring(x.col1,patindex('%,,%',x.col1)+2,len(x.col1)))) y (col1)
-- Substring from the second ',,'
cross apply (values (substring(y.col1,patindex('%,,%',y.col1)+2,len(y.col1)))) z (col1);
And just to reiterate, this is a terrible way to store data, so the best solution is to store it properly.

Answer 2

Here is an alternative solution using charindex. The base idea is the same as in Dale K's an answer, but instead of cutting the string, we specify the start_location for the search by using the third, optional parameter, of charindex. This way, we get the location of each separator, and could slip each value off from the main string.
declare #vtest table (column1 varchar(200))
insert into #vtest ( column1 ) values('dogger1,,dogger2,,dogger3,,dogger4,,dogger5')
insert into #vtest ( column1 ) values('cat1,,cat2,,cat3,,cat4,,cat5')
declare #separetor char(2) = ',,'
select
t.column1
, FI.FirstInstance
, SI.SecondInstance
, TI.ThirdInstance
, iif(TI.ThirdInstance is not null, substring(t.column1, SI.SecondInstance + 2, TI.ThirdInstance - SI.SecondInstance - 2), null)
from
#vtest t
cross apply (select nullif(charindex(#separetor, t.column1), 0) FirstInstance) FI
cross apply (select nullif(charindex(#separetor, t.column1, FI.FirstInstance + 2), 0) SecondInstance) SI
cross apply (select nullif(charindex(#separetor, t.column1, SI.SecondInstance + 2), 0) ThirdInstance) TI
For transparency, I saved the separator string in a variable.
By default the charindex returns 0 if the search string is not present, so I overwrite it with the value null, by using nullif

Answer 3

IMHO, SQL Server 2016 and its JSON support in the best option here.
SQL
-- DDL and sample data population, start
DECLARE #tbl TABLE (ID INT IDENTITY PRIMARY KEY, Tokens VARCHAR(500));
INSERT INTO #tbl VALUES
('cat1,,cat2,,cat3,,cat4,,cat5'),
('dogger1,,dogger2,,dogger3,,dogger4,,dogger5');
-- DDL and sample data population, end
WITH rs AS
(
SELECT *
, '["' + REPLACE(Tokens
, ',,', '","')
+ '"]' AS jsondata
FROM #tbl
)
SELECT rs.ID, rs.Tokens
, JSON_VALUE(jsondata, '$[2]') AS ThirdToken
FROM rs;
Output
+----+---------------------------------------------+------------+
| ID | Tokens | ThirdToken |
+----+---------------------------------------------+------------+
| 1 | cat1,,cat2,,cat3,,cat4,,cat5 | cat3 |
| 2 | dogger1,,dogger2,,dogger3,,dogger4,,dogger5 | dogger3 |
+----+---------------------------------------------+------------+

Answer 4

It´s the same as #"Yitzhak Khabinsky" but i think it looks clearer
WITH CTE_Data
AS(
SELECT 'cat1,,cat2,,cat3,,cat4,,cat5' AS [String]
UNION
SELECT 'dogger1,,dogger2,,dogger3,,dogger4,,dogger5' AS [String]
)
SELECT
A.[String]
,Value3 = JSON_VALUE('["'+ REPLACE(A.[String], ',,', '","') + '"]', '$[2]')
FROM CTE_Data AS A