MySql get list of unique words from table where values in a field separated with comma

Question

I am not sure if this is possible with pure SQL (MySQL) but I will ask anyway. I have a table like this:

ID    TAGS
-----------------------------
1     word1         


        

Answer 1

You can do this in SQL, although it is not pretty.

select distinct reverse(substring_index(reverse(substring_index(tags, ',', n.n)), ',', 1)) as word
from t cross join
     (select 1 as n union all select 2 as n union all select 3 as n union all select 4 as n) n
having word is not null

You need to be sure that the subquery n has at least the number of words in each tags.

Here is the SQLFiddle that demonstrates this.

This is cross joining the original data with sequential numbers. It then picks out the nth value from the tags strings, using substring_index().

To get the maximum number of tags, you can do:

select max(length(tags) - length(replace(tags, ',', 1))+1
from t