Retrieve Distinct concat values from MySQL table - mysql

Question

I have an SQL table advert
id name cat
11 abc ab
12 acb ab, bc
13 abb bcd
14 abcd ad
15 acbd de
16 abbd ad
On using DISTINCT function I am getting an output like this
Query:
SELECT DISTINCT cat FROM advert;
Output:
ab
ab, bc
bcd
ad
de
WHAT changes do I need to make in my query for output like this
ab
bc
bcd
ad
de

Answer 1

select distinct trim(substring_index(substring_index(cat,',',n),',',-1)) as cat
from t join (select 1 as n union all select 2 union all select 3) r
on cat like concat('%',repeat(',%',n-1))

Answer 2

I think you should change your table structure and make it like this.
tblName
id | name
11 abc
12 acb
13 abb
14 abcd
15 acbd
16 abbd
tblCat
id | name_id | cat
some ids* 11 ab
12 ab
12 bc
13 bcd
14 ad
15 de
16 ad
In this way you can easily query and manage your data in your tables.

Answer 3

You should fix your data structure so you are not storing comma-delimited lists in columns. That is the wrong way to store data in a relational database . . . as you can see by the problems for answering this simple question. What you want is a junction table.
Sometimes, we are stuck with other peoples bad designs. You say that there are only two or values, then you can do:
select cat
from ((select substring_index(cat, ', ', 1) as cat
from advert
) union all
(select substring_index(substring_index(cat, ', ', 2), ', ', -1) as cat
from advert
where cat like '%, %'
) union all
(select substring_index(substring_index(cat, ', ', 3), ', ', -1) as cat
from advert
where cat like '%, %, %'
)
) c
group by cat;

Answer 4

First... I would create a statement that would turn all the rows into one big massive comma delimited list.
DECLARE #tmp VarChar(max)
SET #tmp = ''
SELECT #tmp = #tmp + ColumnA + ',' FROM TableA
Then use the table valued udf split described by this SO article to turn that massive string back into a table with a distinct clause to ensure that it's unique.
https://stackoverflow.com/a/2837662/261997
SELECT DISTINCT * FROM dbo.Split(',', #tmp)
Full code example:
if object_id('dbo.Split') is not null
drop function dbo.Split
go
CREATE FUNCTION dbo.Split (#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,
SUBSTRING(#s, start, CASE WHEN stop > 0 THEN stop-start ELSE 512 END) AS s
FROM Pieces
)
go
declare #t table (colA varchar(max))
insert #t select '111, 223'
union all select '333'
union all select '444'
union all select '777,999';
select ltrim(rtrim(s.s)) as colC
from #t t
cross apply
dbo.split(',', t.colA) s