sql查询:子查询和联表查询有什么区别,效率、性能等有什么差异?
作业本_ 2015-09-15 11:11:49 例如:SELECT score,(SELECT userName FROM app_student WHERE app_score.user_id = app_student.app_user_id) userName FROM app_score
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SELECT app_score.score,app_student.userName FROM app_score LEFT JOIN app_student ON app_score.user_id = app_student.app_user_id
谢谢!