SQLite 3.27

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CREATE TABLE B (`id` INTEGER, `name` VARCHAR(3), `tablename` VARCHAR(6));
✓
INSERT INTO B
  (`id`, `name`, `tablename`)
VALUES
  ('1', 'abc', 'table1'),
  ('2', 'xyz', 'table2'),
  ('3', 'abc', 'table1'),
  ('4', 'sdf', 'table2'),
  ('5', 'dfg', 'table1');
✓
SELECT tablename, GROUP_CONCAT(id), GROUP_CONCAT(name||'-'||cnt)
FROM (
    SELECT tablename, GROUP_CONCAT(id) id, name, COUNT(*) cnt
    FROM B
    GROUP BY tablename, name
) 
GROUP BY tablename


tablename
GROUP_CONCAT(id)
GROUP_CONCAT(name||'-'||cnt)


table1
1,3,5
abc-2,dfg-1

table2
4,2
sdf-1,xyz-1