sql - Distinct,REGEXP apply to Field and CONCAT_GROUP in MYSQL to remove repeated words to stored procedure -

context:

i've following table(example):

| id  |   name   | country                  | --------------------------------------------- | 1   | cristian | francia,holanda,alemania | | 2   | andrea   | francia,espaÑa,belgica   | | 3   | fabian   | belgica,alemania         | 

i need put countries in field, need there aren't repeat values.

so, i'm trygin following query:

select group_concat(distinct(country))  usuario; 

or using regular expresion :

select group_concat(distinct(country))  usuario group_concat(country) regexp 'somepattern' 

the wrong answer next:

francia,holanda,alemania,francia,espaÑa,belgica,belgica,alemania 

the expected answer is:

francia,holanda,alemania,espaÑa,belgica 

or make stored procedure?

how expected answer, to n values , differing values?

thanks knowledge , time!.

there's no builtin function in mysql.

it's possible boatload of string processing in mysql, it's ugly, , there has known finite limit on number of string values in comma separated list.

here's 1 way distinct list of field values comma separated lists:

select substring_index(substring_index(concat(country,','),',',1),',',-1) fld   mytable having fld <> ''  union select substring_index(substring_index(concat(country,','),',',2),',',-1) fld   mytable having fld <> ''  union select substring_index(substring_index(concat(country,','),',',3),',',-1) fld   mytable having fld <> ''  union select substring_index(substring_index(concat(country,','),',',4),',',-1) fld   mytable having fld <> ''  union select substring_index(substring_index(concat(country,','),',',5),',',-1) fld   mytable having fld <> ''  union select substring_index(substring_index(concat(country,','),',',6),',',-1) fld   mytable having fld <> ''  order 1 

i'll leave exercise figure out that's doing , how works.

now that's each value in separate row, we'd think might want leave way.

it's easy wrap query in query, , use group_concat function, , return single row string value containing comma separated list.