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CREATE TABLE t1 SELECT 1 id UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3;
CREATE TABLE t2 SELECT 1 id UNION ALL SELECT 2 UNION ALL SELECT 2 UNION ALL SELECT 4;
SELECT * FROM (SELECT * FROM t1) t11 JOIN t2 ON t11.id = t2.id;
| id | id |
|---|---|
| 1 | 1 |
| 1 | 1 |
| 2 | 2 |
| 2 | 2 |
SELECT * FROM t2 WHERE id IN ( SELECT id FROM t1 );
| id |
|---|
| 1 |
| 2 |
| 2 |