MySQL 對待 EXISTS 子句時，仍然采用嵌套子查詢的執(zhí)行方式。如下面的 SQL 語句：

SELECT *FROM my_neighbor nLEFT JOIN my_neighbor_apply sraON n.id = sra.neighbor_idAND sra.user_id = 'xxx'WHERE n.topic_status < 4AND EXISTS(SELECT 1FROM message_info mWHERE n.id = m.neighbor_id

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