select ( (select count(*) from @table1 t1 join @table2 t2 on t2.a=t1.a and t2.b=t1.b) - (select count(*) from @table2 t2 join @table1 t1 on t1.a=t2.a and t1.b=t2.b))
SELECT DISTINCT t.api_id, t.campaign_id, c.api_id FROM `teasers_analytic' AS t JOIN 'campaigns_analytic' AS c ON t.campaigns_id = c.api_id WHERE was_boost = 1 A ND created_at > '2021-04-15 00:00:00' AND created_at < '2021-04-15 23:59:59'