modify the values achieved through group_Concat in MySql? - mysql

Question

I have the following [table a]
id res1 res2
1 a f
1 b f
1 b f
1 c f
2 e g
2 e g
2 e g
2 f g
I'm getting the following after doing a group_concat
select
id,
group_concat(case when cnt = 1 then res1 else concat(cnt, ' ', res1) end) as r1,
group_concat(case when cnt = 1 then res2 else concat(cnt, ' ', res2) end) as r2
from
(
select id, res1,res2, count(*) as cnt
from [table a]
group by id, res1,res2
) t
group by id;
id r1 r2
1 a,2 b,c f,2 f,f
2 3 e,f 3 g,g
The res1 column is coming fine BUT res2 column is duplicating the res1 column.
Basically i want to print the value of how many times a character occurs before the character.
.I want in the following format..
id r1 r2
1 a,2 b,c 4 f
2 3 e,f 4 g
How can I achieve it ?

Answer 1

The way I would approach this is to do two rollups/aggregations, using two separate subqueries for the res1 and res2 columns. The first aggregation is over id and res1 (or res2), and obtains the counts for each letter or word. Then, aggregate again, this time only over the id, to obtain a comma separated string for each id. Finally, join these subqueries together to obtain the final result.
SELECT
t1.id, t1.r1, t2.r2
FROM
(
SELECT t.id, GROUP_CONCAT(res1agg ORDER BY res1) AS r1
FROM
(
SELECT
id,
res1,
CASE WHEN COUNT(*) = 1 THEN res1
ELSE CONCAT(CAST(COUNT(*) AS CHAR(50)), res1) END AS res1agg
FROM yourTable
GROUP BY id, res1
) t
GROUP BY t.id
) t1
INNER JOIN
(
SELECT t.id, GROUP_CONCAT(res2agg ORDER BY res2) AS r2
FROM
(
SELECT
id,
res2,
CASE WHEN COUNT(*) = 1 THEN res2
ELSE CONCAT(CAST(COUNT(*) AS CHAR(50)), res2) END AS res2agg
FROM yourTable
GROUP BY id, res2
) t
GROUP BY t.id
) t2
ON t1.id = t2.id;
Output:
Demo here:
Rextester

Answer 2

Just added 2 more conditions in your query without using more inner queries.
Try this:-
input:-
CREATE TABLE Table1 (id INT, res1 varchar(20), res2 varchar(20));
insert into Table1 values(1, 'a', 'f');
insert into Table1 values(1, 'b', 'f');
insert into Table1 values(1, 'b', 'f');
insert into Table1 values(1, 'c', 'f');
insert into Table1 values(2, 'e', 'g');
insert into Table1 values(2, 'e', 'g');
insert into Table1 values(2, 'e', 'g');
insert into Table1 values(2, 'f', 'g');
Query:-
Select t.id,group_concat(case when cnt = 1 then res1 else concat(cnt, ' ', res1) end) as r1,
case when id=1 then trim(concat(sum(case when id = 1 then cnt end),' ',res2))
else trim(concat(sum(case when id = 2 then cnt end),' ',res2)) end as r2
from
(
select id, res1,res2,count(*) as cnt
from table1 a
group by id, res1,res2
) t
group by t.id
My Output:-
id r1 r2
1 a,c,2 b 4 f
2 f,3 e 4 g
Let me know if you have any questions