What is the best way to join between two table which have coma seperated columns - sql

Question

Table1
ID Name Tags
----------------------------------
1 Customer1 Tag1,Tag5,Tag4
2 Customer2 Tag2,Tag6,Tag4,Tag11
3 Customer5 Tag6,Tag5,Tag10
and Table2
ID Name Tags
----------------------------------
1 Product1 Tag1,Tag10,Tag6
2 Product2 Tag2,Tag1,Tag5
3 Product5 Tag1,Tag2,Tag3
what is the best way to join Table1 and Table2 with Tags column?
It should look at the tags column which coma seperated on table 2 for each coma seperated tag on the tags column in the table 1
Note: Tables are not full-text indexed.

Answer 1

The best way is not to have comma separated values in a column. Just use normalized data and you won't have trouble with querying like this - each column is supposed to only have one value.
Without this, there's no way to use any indices, really. Even a full-text index behaves quite different from what you might thing, and they are inherently clunky to use - they're designed for searching for text, not meaningful data. In the end, you will not get much better than something like
where (Col like 'txt,%' or Col like '%,txt' or Col like '%,txt,%')
Using a xml column might be another alternative, though it's still quite a bit silly. It would allow you to treat the values as a collection at least, though.

Answer 2

I don't think there will ever be an easy and efficient solution to this. As Luaan pointed out, it is a very bad idea to store data like this : you lose most of the power of SQL when you squeeze what should be individual units of data into a single cell.
But you can manage this at the slight cost of creating two user-defined functions. First, use this brilliant recursive technique to split the strings into individual rows based on your delimiter :
CREATE FUNCTION dbo.TestSplit (#sep char(1), #s varchar(512))
RETURNS table
AS
RETURN (
WITH Pieces(pn, start, stop) AS (
SELECT 1, 1, CHARINDEX(#sep, #s)
UNION ALL
SELECT pn + 1, stop + 1, CHARINDEX(#sep, #s, stop + 1)
FROM Pieces
WHERE stop > 0
)
SELECT pn AS SplitIndex,
SUBSTRING(#s, start, CASE WHEN stop > 0 THEN stop-start ELSE 512 END) AS SplitPart
FROM Pieces
)
Then, make a function that takes two strings and counts the matches :
CREATE FUNCTION dbo.MatchTags (#a varchar(512), #b varchar(512))
RETURNS INT
AS
BEGIN
RETURN
(SELECT COUNT(*)
FROM dbo.TestSplit(',', #a) a
INNER JOIN dbo.TestSplit(',', #b) b
ON a.SplitPart = b.SplitPart)
END
And that's it, here is a test roll with table variables :
DECLARE #A TABLE (Name VARCHAR(20), Tags VARCHAR(100))
DECLARE #B TABLE (Name VARCHAR(20), Tags VARCHAR(100))
INSERT INTO #A ( Name, Tags )
VALUES
( 'Customer1','Tag1,Tag5,Tag4'),
( 'Customer2','Tag2,Tag6,Tag4,Tag11'),
( 'Customer5','Tag6,Tag5,Tag10')
INSERT INTO #B ( Name, Tags )
VALUES
( 'Product1','Tag1,Tag10,Tag6'),
( 'Product2','Tag2,Tag1,Tag5'),
( 'Product5','Tag1,Tag2,Tag3')
SELECT * FROM #A a
INNER JOIN #B b ON dbo.MatchTags(a.Tags, b.Tags) > 0

Answer 3

I developed a solution as follows:
CREATE TABLE [dbo].[Table1](
Id int not null,
Name nvarchar(250) not null,
Tag nvarchar(250) null,
) ON [PRIMARY]
GO
CREATE TABLE [dbo].[Table2](
Id int not null,
Name nvarchar(250) not null,
Tag nvarchar(250) null,
) ON [PRIMARY]
GO
get sample data for Table1, it will insert 28000 records
INSERT INTO Table1
SELECT CustomerID,CompanyName, (FirstName + ',' + LastName)
FROM AdventureWorks.SalesLT.Customer
GO 3
sample data for Table2.. i need same tags for Table2
declare #tag1 nvarchar(50) = 'Donna,Carreras'
declare #tag2 nvarchar(50) = 'Johnny,Caprio'
get sample data for Table2, it will insert 9735 records
INSERT INTO Table2
SELECT ProductID,Name, (case when(right(ProductID,1)>=5) then #tag1 else #tag2 end)
FROM AdventureWorks.SalesLT.Product
GO 3
My Solution
create TABLE #dt (
Id int IDENTITY(1,1) PRIMARY KEY,
Tag nvarchar(250) NOT NULL
);
I've create temp table and i will fill with Distinct Tag-s in Table1
insert into #dt(Tag)
SELECT distinct Tag
FROM Table1
Now i need to vertical table for tags
create TABLE #Tags ( Tag nvarchar(250) NOT NULL );
Now i'am fill #Tags table with While, you can use Cursor but while is faster
declare #Rows int = 1
declare #Tag nvarchar(1024)
declare #Id int = 0
WHILE #Rows>0
BEGIN
Select Top 1 #Tag=Tag,#Id=Id from #dt where Id>#Id
set #Rows =##RowCount
if #Rows>0
begin
insert into #Tags(Tag) SELECT Data FROM dbo.StringToTable(#Tag, ',')
end
END
last step : join Table2 with #Tags
select distinct t.*
from Table2 t
inner join #Tags on (',' + t.Tag + ',') like ('%,' + #Tags.Tag + ',%')
Table rowcount= 28000 Table2 rowcount=9735 select is less than 2 second

Answer 4

I use this kind of solution with paths of trees. First put a comma at the very begin and at the very end of the string. Than you can call
Where col1 like '%,' || col2 || ',%'
Some database index the column also for the like(postgres do it partially), therefore is also efficient. I don't know sqlserver.