configurazione
create table overly_complex_tags
(
id integer primary key not null,
tags varchar(100) not null
);
insert into overly_complex_tags
( id, tags )
values
( 3 , 'x,yz,z,x,x' ),
( 5 , 'a,b,c d,a,b,c d,d' )
;
create view digits_v
as
SELECT 0 AS N
UNION ALL
SELECT 1
UNION ALL
SELECT 2
UNION ALL
SELECT 3
UNION ALL
SELECT 4
UNION ALL
SELECT 5
UNION ALL
SELECT 6
UNION ALL
SELECT 7
UNION ALL
SELECT 8
UNION ALL
SELECT 9
;
interroga l'eliminazione dei tag duplicati
update overly_complex_tags t
inner join
(
select id, group_concat(tag) as new_tags
from
(
select distinct t.id, substring_index(substring_index(t.tags, ',', n.n), ',', -1) tag
from overly_complex_tags t
cross join
(
select a.N + b.N * 10 + 1 n
from digits_v a
cross join digits_v b
order by n
) n
where n.n <= 1 + (length(t.tags) - length(replace(t.tags, ',', '')))
) cleaned_tags
group by id
) updated_tags
on t.id = updated_tags.id
set t.tags = updated_tags.new_tags
;
produzione
+----+-----------+
| id | tags |
+----+-----------+
| 3 | yz,z,x |
| 5 | c d,a,d,b |
+----+-----------+
nota
