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create table foo ( cid int, entity_type varchar(25), entity_id int, comment varchar(100) ); insert into foo values (1, 'node', 1, 'initial comment on node with id 1'), (2, 'comment', 1, 'reply to comment with id 1'), (3, 'comment', 2, 'reply to comment with id 2'), (4, 'comment', 1, 'second reply on first comment'), (5, 'node', 2, 'comment on another node'), (6, 'node', 1, 'second direct child comment on node 1'), (7, 'node', 3, 'comment on a third node')
CREATE TABLE
INSERT 0 7
with recursive cte as ( select entity_id, cid from foo where entity_type='node' union all select cte.entity_id, foo.cid from cte join foo on foo.entity_type='comment' and foo.entity_id = cte.cid ) select entity_id, count(*) "#comments" from cte where entity_id in (1,2) group by entity_id
entity_id
#comments
1
5
2
1
SELECT 2