mysql - EXISTS 行数

Question

SELECT * FROM table1 WHERE EXISTS (SELECT * FROM table2 WHERE *condition*)

例如，我可以检查是否有 3 行符合 table2 条件吗？ 所以像

[...]WHERE EXISTS 3 (SELECT[...]

谢谢

Answer 1

您可以使用 exists 之外的其他内容来执行此操作。例如，聚合 table2 并计算行数:

SELECT *
FROM table1 t1 JOIN
     (SELECT t2.??
      FROM table2 t2
      WHERE conditions (no correlation conditions)
      GROUP BY t2.??
      HAVING COUNT(*) >= 3
     ) t2
     ON t1.?? = t2.??;