本文通过两个SQL语句示例介绍了如何使用EXISTS关键字来筛选满足特定子查询条件的记录。第一个示例展示了当外部查询的ID存在于内部查询中时返回所有字段；第二个示例则展示了当外部查询的ID不存在于内部查询中时返回所有字段。
语法规则：
SELECT * FROM tableName t WHERE 1 = 1 AND 2 = 2 AND EXISTS (SELECT * FROM tableName t2 WHERE t.id = t2.proj_id)
SELECT * FROM tableName t WHERE 1 = 1 AND 2 = 2 AND NOT EXISTS (SELECT * FROM tableName t2 WHERE t.id = t2.proj_id)
SELECT * FROM tableName t WHERE 1 = 1 AND 2 = 2 AND NOT EXISTS (SELECT * FROM tableName t2 WHERE t.id = t2.proj_id)
转载于:https://www.cnblogs.com/andremao/p/7860399.html
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